Fine root dry matter relative to mango (Mangifera indica) tree scion size grafted on size-controlling rootstocks, is negatively related to scion growth rate

Knowledge of root dry matter (DM) allocation, in relation to differing vigour conferred by rootstock cultivars, is required to understand the structural relationships between rootstock and scion. We investigated the mass of roots (four size classes up to 23 mm diameter) by coring proximal to five polyembryonic mango rootstock cultivars known to differ in their effects on the vigour and productivity of scion cultivar ‘Kensington Pride’, in a field trial of 13-year-old trees. Significant differences in fine (<0.64 and 0.64–1.88 mm diameter) and small (1.88–7.50 mm) root DM contents were observed between rootstock cultivars. There was a complex relationship between the amount of feeder (fine and small size classes) roots and scion size (trunk cross sectional area, TCSA), with intermediate size trees on rootstock MYP having the most feeder roots, while the smallest trees, on the rootstock Vellaikulamban had the least of these roots. Across rootstock cultivars, tree vigour (TCSA growth rate) was negatively and significantly related to the ratio of fine root DM/scion TCSA, suggesting this may be a useful indicator of the vigour that different rootstocks confer on the scion. In contrast non-ratio root DM and scion TCSA results had no significant relationships. The significant rootstock effects on orchard root growth and tree size could not be predicted from earlier differences in nursery seedling vigour, nor did seedling vigour predict root DM allocation.

Non-destructive prediction of 'Hass' avocado dry matter via FT-NIR spectroscopy.

BACKGROUND: The inability to consistently guarantee internal quality of horticulture produce is of major importance to the primary producer, marketers and ultimately the consumer. Currently, commercial avocado maturity estimation is based on the destructive assessment of percentage dry matter (%DM), and sometimes percentage oil, both of which are highly correlated with maturity. In this study the utility of Fourier transform (FT) near-infrared spectroscopy (NIRS) was investigated for the first time as a non-invasive technique for estimating %DM of whole intact 'Hass' avocado fruit. Partial least squares regression models were developed from the diffuse reflectance spectra to predict %DM, taking into account effects of intra-seasonal variation and orchard conditions. RESULTS: It was found that combining three harvests (early, mid and late) from a single farm in the major production district of central Queensland yielded a predictive model for %DM with a coefficient of determination for the validation set of 0.76 and a root mean square error of prediction of 1.53% for DM in the range 19.4-34.2%. CONCLUSION: The results of the study indicate the potential of FT-NIRS in diffuse reflectance mode to non-invasively predict %DM of whole 'Hass' avocado fruit. When the FT-NIRS system was assessed on whole avocados, the results compared favourably against data from other NIRS systems identified in the literature that have been used in research applications on avocados.

Effect of irrigation amounts applied with subsurface drip irrigation on corn evapotranspiration, yield, water use efficiency, and dry matter production in a semiarid climate

Quantifying the local crop response to irrigation is important for establishing adequate irrigation management strategies. This study evaluated the effect of irrigation applied with subsurface drip irrigation on field corn (Zea mays L.) evapotranspiration (ETc), yield, water use efficiencies (WUE = yield/ETc, and IWUE = yield/irrigation), and dry matter production in the semiarid climate of west central Nebraska. Eight treatments were imposed with irrigation amounts ranging from 53 to 356 mm in 2005 and from 22 to 226 mm in 2006. A soil water balance approach (based on FAO-56) was used to estimate daily soil water and ETc. Treatments resulted in seasonal ETc of 580-663 mm and 466-656 mm in 2005 and 2006, respectively. Yields among treatments differed by as much as 22% in 2005 and 52% in 2006. In both seasons, irrigation significantly affected yields, which increased with irrigation up to a point where irrigation became excessive. Distinct relationships were obtained each season. Yields increased linearly with seasonal ETc (R 2 = 0.89) and ETc/ETp (R 2 = 0.87) (ETp = ETc with no water stress). The yield response factor (ky), which indicates the relative reduction in yield to relative reduction in ETc, averaged 1.58 over the two seasons. WUE increased non-linearly with seasonal ETc and with yield. WUE was more sensitive to irrigation during the drier 2006 season, compared with 2005. Both seasons, IWUE decreased sharply with irrigation. Irrigation significantly affected dry matter production and partitioning into the different plant components (grain, cob, and stover). On average, the grain accounted for the majority of the above-ground plant dry mass (≈59%), followed by the stover (≈33%) and the cob (≈8%). The dry mass of the plant and that of each plant component tended to increase with seasonal ETc. The good relationships obtained in the study between crop performance indicators and seasonal ETc demonstrate that accurate estimates of ETc on a daily and seasonal basis can be valuable for making tactical in-season irrigation management decisions and for strategic irrigation planning and management.

The impact of dry matter, ripeness and internal defects on consumer perceptions of avocado quality and intentions to purchase.

Insights into the relative importance of various aspects of product quality can be provided through quantitative analysis of consumer preference and choice of fruit. In this study, methods previously used to establish taste preferences for kiwifruit (Harker et al., 2008) and conjoint approaches were used to determine the influence of three key aspects of avocado quality on consumer liking and willingness to purchase fruit: dry matter percentage (DM), level of ripeness (firmness) and internal defects (bruising). One hundred and seven consumers tasted avocados with a range of DM levels from ~20% (minimally mature) to nearly 40% (very mature), and at a range of fruit firmness (ripeness) stages (firm-ripe to soft-ripe). Responses to bruising, a common quality defect in fruit obtained from the retail shelf, were examined using a conjoint approach in which consumers were presented with photographs showing fruit affected by damage of varying severity. In terms of DM, consumers showed a progressive increase in liking and intent to buy avocados as the DM increased. In terms of ripeness, liking and purchase intent was higher in avocados that had softened to a firmness of 6.5 N or below (hand-rating 5). For internal defects, conjoint analysis revealed that price, level of bruising and incidence of bruising all significantly lowered consumers' future purchase decision, but the latter two factors had a greater impact than price. These results indicate the usefulness of the methodology, and also provide realistic targets for Hass avocado quality on the retail shelf.

Effects of seasonal variability on FT-NIR prediction of dry matter content for whole Hass avocado fruit

Fourier Transform (FT)-near infra-red spectroscopy (NIRS) was investigated as a non-invasive technique for estimating percentage (%) dry matter of whole intact 'Hass' avocado fruit. Partial least squares (PLS) calibration models were developed from the diffuse reflectance spectra to predict % dry matter, taking into account effects of seasonal variation. It is found that seasonal variability has a significant effect on model predictive performance for dry matter in avocados. The robustness of the calibration model, which in general limits the application for the technique, was found to increase across years (seasons) when more seasonal variability was included in the calibration set. The R-v(2) and RMSEP for the single season prediction models predicting on an independent season ranged from 0.09 to 0.61 and 2.63 to 5.00, respectively, while for the two season models predicting on the third independent season, they ranged from 0.34 to 0.79 and 2.18 to 2.50, respectively. The bias for single season models predicting an independent season was as high as 4.429 but <= 1.417 for the two season combined models. The calibration model encompassing fruit from three consecutive years yielded predictive statistics of R-v(2) = 0.89, RMSEP = 1.43% dry matter with a bias of -0.021 in the range 16.1-39.7% dry matter for the validation population encompassing independent fruit from the three consecutive years. Relevant spectral information for all calibration models was obtained primarily from oil, carbohydrate and water absorbance bands clustered in the 890-980, 1005-1050, 1330-1380 and 1700-1790 nm regions. These results indicate the potential of FT-NIRS, in diffuse reflectance mode, to non-invasively predict the % dry matter of whole 'Hass' avocado fruit and the importance of the development of a calibration model that incorporates seasonal variation. Crown Copyright (c) 2012 Published by Elsevier B.V. All rights reserved.

Stunted cotton (Gossypium hirsutum L.) fully recovers biomass and yield of seed cotton after delayed root inoculation with spores of an arbuscular mycorrhizal fungus (Glomus mosseae)

In the northern grain and cotton region of Australia, poor crop growth after long periods of fallow, called 'long-fallow' disorder, is caused by a decline of natural arbuscular-mycorrhizal fungi (AMF). When cotton was grown in large pots containing 22 kg of Vertisol from a field recently harvested from cotton in Central Queensland, plants in pasteurised soil were extremely stunted compared with plants in unpasteurised soil. We tested the hypothesis that this extreme stunting was caused by the absence of AMF and examined whether such stunted plants could recover from subsequent treatment with AMF spores and/or P fertiliser. At 42 days after sowing, the healthy cotton growing in unpasteurised soil had 48% of its root-length colonised with AMF, whereas the stunted cotton had none. After inoculation with AMF spores (6 spores/g soil of Glomus mosseae) and/or application of P fertiliser (50 mg P/kg soil) at 45 days after sowing, the stunted plants commenced to improve about 25 days after treatment, and continued until their total dry matter and seed cotton production equalled that of plants growing in unpasteurised soil with natural AMF. In contrast, non-mycorrhizal cotton grown without P fertiliser remained stunted throughout and produced no bolls and only 1% of the biomass of mycorrhizal cotton. Even with the addition of P fertiliser, non-mycorrhizal cotton produced only 64% of the biomass and 58% of the seed cotton (lint + seed) of mycorrhizal cotton plants. These results show that cotton is highly dependent on AMF for P nutrition and growth in Vertisol (even with high rates of P fertiliser), but can recover from complete lack of AMF and consequent stunting during at least the first 45 days of growth when treated with AMF spores and/or P fertiliser. This corroborates field observations in the northern region that cotton may recover from long-fallow disorder caused by low initial levels of AMF propagules in the soil as the AMF colonisation of its roots increases during the growing season.

Cotton root systems and recovery of applied P and K fertilisers

With potential to accumulate substantial amounts of above-ground biomass, at maturity an irrigated cotton crop can have taken up more than 20 kg/ha phosphorus and often more than 200 kg/ha of potassium. Despite the size of plant accumulation of P and K, recovery of applied P and K fertilisers by the crop in our field experiment program has poor. Processing large amounts of mature cotton plant material to provide a representative sample for chemical analysis has not been without its challenges, but the questions regarding mechanism of where, how and when the plant is acquiring immobile nutrients remain. Dry matter measured early in the growing season (squaring, first white flower) have demonstrated a 50% increase in crop biomass to applied P (in particular), but it represents only 20% of the total P accumulation by the plant. By first open boll (and onwards), no response in dry matter or P concentration could be detected to P application. A glasshouse study indicated P recovery was greater (to FOB) where it was completely mixed through a profile as opposed to a banded application method suggesting cotton prefers a more diffuse distribution. The relative effects of root morphology, mycorrhizal fungi infection, seasonal growth patterns and how irrigation is applied are areas for future investigation on how, when and where cotton acquires immobile nutrients.

Sustaining productivity of a Vertosol at Warra, Queensland, with fertilisers, no-tillage or legumes. 7. Yield, nitrogen and disease-break benefits from lucerne in a two-year lucerne–wheat rotation

Continuous cultivation and cereal cropping of southern Queensland soils previously supporting native vegetation have resulted in reduced soil nitrogen supply, and consequently decreased cereal grain yields and low grain protein. To enhance yields and protein concentrations of wheat, management practices involving N fertiliser application, with no-tillage and stubble retention, grain legumes, and legume leys were evaluated from 1987 to 1998 on a fertility-depleted Vertosol at Warra, southern Queensland. The objective of this study was to examine the effect of lucerne in a 2-year lucerne–wheat rotation for its nitrogen and disease-break benefits to subsequent grain yield and protein content of wheat as compared with continuous wheat cropping. Dry matter production and nitrogen yields of lucerne were closely correlated with the total rainfall for October–September as well as March–September rainfall. Each 100 mm of total rainfall resulted in 0.97 t/ha of dry matter and 26 kg/ha of nitrogen yield. For the March–September rainfall, the corresponding values were 1.26 t/ha of dry matter and 36 kg/ha of nitrogen yield. The latter values were 10% lower than those produced by annual medics during a similar period. Compared with wheat–wheat cropping, significant increases in total soil nitrogen were observed only in 1990, 1992 and 1994 but increases in soil mineralisable nitrogen were observed in most years following lucerne. Similarly, pre-plant nitrate nitrogen in the soil profile following lucerne was higher by 74 kg/ha (9–167 kg N/ha) than that of wheat–wheat without N fertiliser in all years except 1996. Consequently, higher wheat grain protein (7 out of 9 seasons) and grain yield (4 out of 9 seasons) were produced compared with continuous wheat. There was significant depression in grain yield in 2 (1993 and 1995) out of 9 seasons attributed to soil moisture depletion and/or low growing season rainfall. Consequently, the overall responses in yield were lower than those of 50 kg/ha of fertiliser nitrogen applied to wheat–wheat crops, 2-year medic–wheat or chickpea–wheat rotation, although grain protein concentrations were higher following lucerne. The incidence and severity of the soilborne disease, common root rot of wheat caused by Bipolaris sorokiniana, was generally higher in lucerne–wheat than in continuous wheat with no nitrogen fertiliser applications, since its severity was significantly correlated with plant available water at sowing. No significant incidence of crown rot or root lesion nematode was observed. Thus, productivity, which was mainly due to nitrogen accretion in this experiment, can be maintained where short duration lucerne leys are grown in rotations with wheat.

Assessment of internal quality attributes of mandarin fruit. 1. NIR calibration model development

The utility of near infrared spectroscopy as a non-invasive technique for the assessment of internal eating quality parameters of mandarin fruit (Citrus reticulata cv. Imperial) was assessed. The calibration procedure for the attributes of TSS (total soluble solids) and DM (dry matter) was optimised with respect to a reference sampling technique, scan averaging, spectral window, data pre-treatment (in terms of derivative treatment and scatter correction routine) and regression procedure. The recommended procedure involved sampling of an equatorial position on the fruit with 1 scan per spectrum, and modified partial least squares model development on a 720–950-nm window, pre-treated as first derivative absorbance data (gap size of 4 data points) with standard normal variance and detrend scatter correction. Calibration model performance for the attributes of TSS and DM content was encouraging (typical Rc2 of >0.75 and 0.90, respectively; typical root mean squared standard error of calibration of <0.4 and 0.6%, respectively), whereas that for juiciness and total acidity was unacceptable. The robustness of the TSS and DM calibrations across new populations of fruit is documented in a companion study.

Assessment of internal quality attributes of mandarin fruit. 2. NIR calibration model robustness

The robustness of multivariate calibration models, based on near infrared spectroscopy, for the assessment of total soluble solids (TSS) and dry matter (DM) of intact mandarin fruit (Citrus reticulata cv. Imperial) was assessed. TSS calibration model performance was validated in terms of prediction of populations of fruit not in the original population (different harvest days from a single tree, different harvest localities, different harvest seasons). Of these, calibration performance was most affected by validation across seasons (signal to noise statistic on root mean squared error of prediction of 3.8, compared with 20 and 13 for locality and harvest day, respectively). Procedures for sample selection from the validation population for addition to the calibration population (‘model updating’) were considered for both TSS and DM models. Random selection from the validation group worked as well as more sophisticated selection procedures, with approximately 20 samples required. Models that were developed using samples at a range of temperatures were robust in validation for TSS and DM.

The performance of strawberry plugs in Queensland

Plugs or containerized plants can offer several advantages over traditional bare-rooted runner plants for strawberry (Fragaria x ananassa) production. Some of these benefits include easier planting, better establishment, fewer pests and diseases, and lower water use during plant establishment resulting in less leaching of applied fertilizers. Plugs also offer the potential for mechanical planting. In some areas of Europe and North America, plugs provide earlier production, greater productivity and larger fruit than runners. Research has also shown that the plants can be grown under short days and low temperatures to manipulate flower initiation and fruiting. Plugs are more expensive to buy compared with runner plants, and will only be adopted by industry if the extra costs are matched by convenience, resource conservation, increased fruiting and returns to producers. We investigated the productivity of 'Festival' and 'Sugarbaby' propagated as plugs (75 cm3 containers) and runners from Stanthorpe in southern Queensland (elevation of 872 m), and grown at Nambour on the Sunshine Coast (elevation 29 m). At planting, the plug plants weighed 0.8 ± 0.1 g DW compared with 53 ± 0.5 g DW for the runner plants. 'Sugarbaby' plugs were larger than 'Festival' plugs (33 ± 0.6 g versus 2.9 ± 0.6 g). The differences in growth at planting were maintained until the third week of July (day 94), with the plug plants weighing 17.8 ± 2.2 g, and the runner plants 21.4 ± 23 g. The proportion of plant dry matter allocated to the leaves increased over time from 59 to 70%, while the proportion allocated to the roots decreased from 21 to 10%. Harvest commenced after 60 days, with the plug plants yielding only 60% of the yields of the runner plants up until 8 August or day 109 (14.2 ± 1.4 g plant -1 week-1 versus 23.6 ± 1.9 g plant-1 week-1). 'Festival' (22.2 ± 2.0 g plant-1 week -1) had higher yields than 'Sugarbaby' (15.5 ± 1.5 g plant-1 week-1), even though plants of the latter were larger. Average fruit weight was 15.6 ± 0.3 g, with no effect of cultivar, plant type or harvest time. In other words, the differences in yield between the various treatments were due to differences in fruit set The lower yields of the plug plants probably reflect their small size at planting. Future research should determine whether plugs grown in larger cells (150 to 300 cm3 as in the USA and Europe) are more productive. Tips to be grown in larger containers should be harvested earlier than those for small cells to maximize root growth of the plug plant. This will probably extend the time required from harvest of the tips and potting them from the current four to five weeks, to eight to ten weeks.

Effect of defoliation interval and height on the growth and quality of Arachis pintoi cv. Amarillo

The effect of defoliation on Amarillo (Arachis pintoi cv. Amarillo) was studied in a glasshouse and in mixed swards with 2 tropical grasses. In the glasshouse, Amarillo plants grown in pots were subjected to a 30/20°C or 25/15°C temperature regime and to defoliation at 10-, 20- or 30-day intervals for 60 days. Two field plot studies were conducted on Amarillo with either irrigated kikuyu (Pennisetum clandestinum) in autumn and spring or dryland Pioneer rhodes grass (Chloris gayana) over summer and autumn. Treatments imposed were 3 defoliation intervals (7, 14 and 28 days) and 2 residual heights (5 and 10 cm for kikuyu; 3 and 10 cm for rhodes grass) with extra treatments (56 days to 3 cm for both grasses and 21 days to 5 cm for kikuyu). Defoliation interval had no significant effect on accumulated Amarillo leaf dry matter (DM) at either temperature regime. At the higher temperature, frequent defoliation reduced root dry weight (DW) and increased crude protein (CP) but had no effect on stolon DW or in vitro organic matter digestibility (OMD). On the other hand, at the lower temperature, frequent defoliation reduced stolon DW and increased OMD but had no effect on root DW or CP. Irrespective of temperaure and defoliation, water-soluble carbohydrate levels were higher in stolons than in roots (4.70 vs 3.65%), whereas for starch the reverse occured (5.37 vs 9.44%). Defoliating the Amarillo-kikuyu sward once at 56 days to 3 cm produced the highest DM yield in autumn and sprong (582 and 7121 kg/ha DM, respectively), although the Amarillo component and OMD were substantially reduced. Highest DM yields (1726 kg/ha) were also achieved in the Amarillo-rhodes grass sward when defoliated every 56 days to 3 cm, although the Amarillo component was unaffected. In a mixed sward with either kikuyu or rhodes grass, the Amarillo component in the sward was maintained up to a 28-day defoliation interval and was higher when more severely defoliated. The results show that Amarillo can tolerate frequent defoliation and that it can co-exist with tropical grasses of differing growth habits, provided the Amarillo-tropical grass sward is subject to frequent and severe defoliation.

Salinity tolerance of twelve hybrid Bermudagrass (Cynodon Dactylon (L.) Pers. x C. Transvaalensis Burtt Davy) genotypes

Salinity is an increasingly important issue in both rural and urban areas throughout much of Australia. The use of recycled/reclaimed water and other sources of poorer quality water to irrigate turf is also increasing. Hybrid Bermudagrass (Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt Davey), together with the parent species C. dactylon, are amongst the most widely used warm-season turf grass groups. Twelve hybrid Bermudagrass genotypes and one accession each of Bermudagrass (C. dactylon), African Bermudagrass (C. transvaalensis) and seashore paspalum (Paspalum vaginatum Sw.) were grown in a glasshouse experiment with six different salinity treatments applied hydroponically through the irrigation water (ECW = <0.1, 6, 12, 18, 24 or 30 dSm-1) in a flood-and-drain system. Each pot was clipped progressively at 2-weekly intervals over the 12-week experimental period to determine dry matter production; leaf firing was rated visually on 3 occasions during the last 6 weeks of salinity treatment. At the end of the experiment, dry weights of roots and crowns below clipping height were also determined. Clipping yields declined sharply after about the first 6 weeks of salinity treatment, but then remained stable at substantially lower levels of dry matter production from weeks 8 to 12. Growth data over this final 4-week experimental period is therefore a more accurate guide to the relative salinity tolerance of the 15 entries than data from the preceding 8 weeks. Based on these data, the 12 hybrid Bermudagrass genotypes showed moderate salinity tolerance, with FloraDwarfM, 'Champion Dwarf', NovotekM and 'TifEagle' ranking as the most salt tolerant and 'Patriot', 'Santa Ana', 'Tifgreen' and TifSport M the least tolerant within the hybrid group. Nevertheless, Santa Ana, for example, maintained relatively strong root growth as salinity increased, and so may show better salt tolerance in practice than predicted from the growth data alone. The 12 hybrid Bermudagrasses and the single African Bermudagrass genotype were all ranked above FloraTeXM Bermudagrass in terms of salt tolerance. However, seashore paspalum, which is widely acknowledged as a halophytic species showing high salt tolerance, ranked well above all 14 Cynodon genotypes in terms of salinity tolerance.

Characterisation of sweetpotato from Papua New Guinea and Australia: Physicochemical, pasting and gelatinisation properties.

The physicochemical and functional properties of flours from 25 Papua New Guinean and Australian sweetpotato cultivars were evaluated. The cultivars (white-, orange-, cream-, and purple-fleshed, and with dry matter, from 15 to 28 g/100 g), were obovate, oblong, elliptic, curved, irregular in shape, and essentially thin-cortexed (1-2 mm). Flour yield was less than 90 g/100 g solids, while starch, protein, amylose, water absorption and solubility indices, as well as total sugars, varied significantly (p < 0.05). Potassium, sodium, calcium, and phosphorus were the major minerals measured, and there were differences in the pasting properties, which showed four classes of shear-thinning and shear-thickening behaviours. Differential scanning calorimetry showed single-stage gelatinisation behaviour, with cultivar-dependent temperatures (61-84 degrees C) and enthalpies (12-27 J/g dry starch). Oval-, round- and angular-shaped granules were observed with a scanning electron microscope, while X-ray diffraction revealed an A-type diffraction pattern in the cultivars, with about 30% crystallinity. This study shows a wide range of sweetpotato properties, reported for the first time.

QTL for nodal root angle in sorghum (Sorghum bicolor L. Moench) co-locate with QTL for traits associated with drought adaptation.

Nodal root angle in sorghum influences vertical and horizontal root distribution in the soil profile and is thus relevant to drought adaptation. In this study, we report for the first time on the mapping of four QTL for nodal root angle (qRA) in sorghum, in addition to three QTL for root dry weight, two for shoot dry weight, and three for plant leaf area. Phenotyping was done at the six leaf stage for a mapping population (n = 141) developed by crossing two inbred sorghum lines with contrasting root angle. Nodal root angle QTL explained 58.2% of the phenotypic variance and were validated across a range of diverse inbred lines. Three of the four nodal root angle QTL showed homology to previously identified root angle QTL in rice and maize, whereas all four QTL co-located with previously identified QTL for stay-green in sorghum. A putative association between nodal root angle QTL and grain yield was identified through single marker analysis on field testing data from a subset of the mapping population grown in hybrid combination with three different tester lines. Furthermore, a putative association between nodal root angle QTL and stay-green was identified using data sets from selected sorghum nested association mapping populations segregating for root angle. The identification of nodal root angle QTL presents new opportunities for improving drought adaptation mechanisms via molecular breeding to manipulate a trait for which selection has previously been very difficult.