Discrimination among host plants (Leucaena species and accessions) by the psyllid pest Heteropsylla cubana and implications for understanding resistance

1 The herbivorous bug Heteropsylla cubana Crawford (Homoptera: Psyllidae) is a pest of the cattle fodder crop Leucaena (Leguminosae: Mimosoideae). The interaction between the psyllid and three varieties of its Leucaena host plant was investigated in relation to the apparent resistance of some Leucaena varieties (Leucaena leucocephala, Leucaena pallida and their hybrids) to attack. 2 Field trials demonstrated that adult psyllids distinguished among the different varieties of Leucaena over a distance, and were attracted to L. leucocephala in significantly higher numbers than to L. pallida or to the hybrid. Pesticide treatment increased the attractiveness of Leucaena plants, even of those deemed to be psyllid resistant. Numbers of psyllid eggs and nymphs, sampled in the field, reflect the arrival rates of adults at the three plant varieties. 3 Wavelength reflectance data of the three Leucaena varieties were not significantly different from one another, suggesting that psyllids cannot discriminate among the three plants using brightness or wavelength cues. There was a differential release of caryophyllene among the three varieties. Release of caryophyllene in L. leucocephala and the hybrid appeared to be influenced by environmental conditions. 4 Experiments demonstrated that caryophyllene (at least on its own) did not influence the behaviour of leucaena psyllids in relation to leucaena plants. 5 The results suggest that host plant volatiles cannot be dismissed as significant in the interaction between the leucaena psyllid and its Leucaena host plants. Further avenues for investigation are recommended and these are related to novel ways of understanding resistance in insect plant inter-relationships.

Animal production potential of some new Leucaena accessions in the Markham valley, Papua New Guinea

Signal grass pastures were oversown with four Leucaena spp. planted in hedgerows and evaluated for their agronomic productivity and ability to support steer liveweight gains. Each Leucaena sp. (L. leucocephala, L. pallida, L colli. nst. i., L. trichandra) was planted as seedlings into two I ha paddocks in rows 5 m apart, with I m spacing between trees. Cattle were rotationally grazed on the 2 replicates of each species, as well as on two I ha paddocks of a signal grass on y (Brachiaria decumbens) control, over a 243-day period at a stocking rate of 3 steers/ha. Mean presentation yield and herbage allowance of the Leucaena accessions over the grazing period were highest for L pallida (1100 kg/ha and 0.8 kg DM/kg LW, respectively), followed by L. leucocephala (700 kg/ha and 0.5 kg DM/kg LW), L. collinsii (700 kg/ha and 0.4 kg DM/kg LW) and L. trichandra (300 kg/ha and 0.2 kg DM/kg LW). Despite only moderate presentation yields and herbage allowances, steers grazing L. leucocephala and L. collinsii accessions produced the highest mean liveweight gains (LWG) of 0. and 0.56 kg/hd/d, respectively. While L. pallida produced the highest DM yields, it supported the lowest LWG of 0.36 kg/hd/d. The mean LWGs of steers grazing L. trichandra and the control (grass only) treatments were similar at 0.48 kg/ hd/d. The possible reasons for the differences in steer performance on the different Leucaena accessions are discussed.

Rainfall salt accessions in the Queensland Murray-Darling Basin

Two east - west transects were established in southern Queensland to quantify rainfall inputs of chloride and associated ions. Electrical conductivity, pH, and major and minor ions were measured at 9 sites within the Queensland Murray - Darling Basin and 1 site to the east. Variability at some sites was high, possibly a function of the sample collection method. Ionic concentrations decreased with distance inland, a trend similar to that observed elsewhere in Australia, although values closer to the coast were higher than observed in southern and western Australia. Equations to predict both annual average rainfall chloride mass deposition and total salt deposition were derived.

Root and shoot attributes of indigenous perennial accessions of the wild mungbean (Vigna radiata ssp sublobata)

Root and shoot attributes of 12 indigenous perennial accessions of the wild mungbean (Vigna radiata ssp. sublobata) were evaluated in early and late summer sowings in the field in SE Queensland. All but one of the accessions were obtained from the Townsville-Charters Towers region of NE Queensland. In both sowings, the accessions developed thickened tap and lateral roots, the taproot thickening extending to a depth of 0.20-0.30m below the soil surface, depending on accession. The thickened lateral roots emerged from the taproot within 0.10m of the soil surface, and extended laterally up to 1.10 m, remaining close to the soil surface. Differences among the accessions in gross root morphology and phenology were relatively small. There were differences among the accessions in the production of seed, tuberised root, and recovered total plant biomass. Depending on accession and sowing date, the tuberised roots accounted for up to 31% of recovered plant biomass and among accessions, the root biomass was positively correlated with total plant biomass. In contrast, seed biomass represented only a small proportion of recovered plant biomass, up to a maximum of 14%, depending on accession and sowing date. Among accessions, the proportion of seed biomass tended to be negatively correlated with that of tuber biomass. The perennial trait appears to be unique to Australian accessions of wild mungbean obtained from coastal-subcoastal, speargrass-dominant woodlands of NE Queensland. Although the ecological significance of the trait remains conjectural, field observation indicates that it facilitates rapid plant re-growth following early summer rainfall, especially where dry-season. re has removed previous-season above-ground growth.

Variation among Australian accessions of the wild mungbean (Vigna radiata ssp sublobata) for traits of agronomic, adaptive, or taxonomic interest

The wild mungbean, Vigna radiata ssp. sublobata, is an 'old world' tropical species indigenous throughout the better watered areas of northern Australia. Variation among 115 accessions, mainly from Australia, West Timor, and Papua New Guinea, was evaluated for several diverse traits. The plants were cultivated in the field at 2 sowing dates, at both a tropical and a subtropical location, with 6 accessions from India and a mungbean cultivar for comparison. Substantial variation was identified for traits of potential agronomic, adaptive, or taxonomic interest. For some traits, like phenology, the variation appeared to be systematic, with plausible underlying physiological and/or adaptive explanation. Among accessions, wild type traits, like prostrate habit, more gracile morphology, twining form, and small hard seeds, tended to be associated. There was a general geographic trend for lines collected from locations more remote from where mungbean has historically been cultivated to show greater expression of wild type traits, with few 'traits of domestication' evident in the Australian accessions. Some of the identified variation, e. g. higher seed protein content, hardseededness, and putative disease resistance, may be of value in mungbean variety improvement. A more targetted evaluation of the collection would likely reveal other adaptations, especially tolerance to environmental stresses. As such, the wild accessions are a potentially valuable if under-utilised germplasm resource.

Ecosystem dynamics at disturbed and undisturbed sites in North Queensland wet tropical rain forest. III. Nutrient returns to the forest floor through litterfall

The nutrient contents and accessions in litterfall over a period of 3 y are reported for undisturbed areas and at two sites disturbed by selective harvesting in tropical rain forest in North Queensland, Australia. Mean concentrations (mg g(-1) dry weight) of nutrients in litterfall ranged from 10 to 12 for nitrogen; 0.33 to 0.43 for phosphorus; 3.6 to 4.3 for potassium; 6.0 to 10.5 for calcium and 1.7 to 2.6 for magnesium. These concentrations are in the middle to lower part of the spectrum of values recorded for tropical forest. Accessions of nutrients in litterfall (kg ha(-1) y(-1)) ranged from 59 to 64 N; 1.9 to 2.4 P; 20 to 24K; 34 to 63 Ca; and 9 to 16 Mg. These rates, particularly for IN and P, are among the lowest recorded for tropical forests. There were no consistent between-site differences in total nutrient accessions in small litterfall. In terms of the contribution of litterfall to the accessions of nutrients to the forest floor, this suggests that the logged sites have recovered from the effects of selective harvesting within 25 y. Nutrient accessions at each site were distinctly seasonal, with maximum accessions occurring in the late dry season to late in the wet season. Leaf-fall accounted for the largest proportion of nutrient accessions over the study period, although at certain times accessions in both reproductive material and wood were significant. A cyclone which crossed the coast near the study sites resulted in large nutrient accessions over a short period but had little effect on the total annual accession. A comparison with previous studies of litterfall in Australian tropical rainforests indicates that nutrient return in litterfall is directly related to soil fertility.

Adaptation of sorghum: characterisation of genotypic flowering responses to temperature and photoperiod

Sorghum [Sorghum bicolor (L.) Moench] is an important cereal crop grown in a wide range of tropical and temperate environments. This study was conducted to characterise the photothermal flowering responses of sorghum genotypes and to examine relationships between photothermal characteristics and environment of origin in order to better understand the phenological basis of adaptation to environment in sorghum. Twenty-four germplasm accessions and one hybrid from 24 major sorghum-growing areas were grown in a wide range of environments varying in temperature and photoperiod in India, Kenya and Mall between 1992 and 1995. Times from sowing to flowering (f) were recorded, and the responsiveness of 1/f to temperature and photoperiod was quantified using photothermal models. Times from sowing to flowering were accurately predicted in a wide range of environments using a multiplicative rate photothermal model. Significant variation in the minimum time to flower (F-m) and photoperiod sensitivity (critical photoperiod, P-c, and photoperiod-sensitivity slope, P-s) was observed among the genotypes; in contrast there was little variation in base temperature (Tb) Adaptation of sorghum to the diverse environments in which it is grown was largely determined by photoperiod sensitivity and minimum time to flower; photoperiod sensitivity determines bread adaptation to latitude (daylength), while variation in the minimum time to flower determines specific adaptation within smaller ranges of latitude, e.g. within the humid and sub-humid tropics.

Characterisation of Leucaena condensed tannins by size and protein precipitation capacity

The ability of differently sized condensed tannins from the genus Leucaena, a fodder tree-legume, to bind protein at different pH values was evaluated to characterise their potential biological effects. Two factors affecting the ability of condensed tannin to bind protein, its major biological activity, have been purported to be the condensed tannin size and the pH of the reaction environment. To test these hypotheses, the protein-precipitating capacities of condensed tannin extracted from four Leucaena genotypes, L leucocephala (UHK636), L pallida (CQ3439), L trichandra (CP146568) and L collinsii (OFI52/88), were assessed. Condensed tannin from L leucocephala had approximately 50% of the ability to precipitate protein on a gg(-1) basis than L pallida or L trichandra, while L collinsii gave no measurable ability to precipitate protein (reaction environment pH 5.0). Increasing or decreasing the pH of the reaction solution away from pH 5.0 (approximately the isoelectric point of the protein) reduced the ability of condensed tannin from all the species to precipitate protein, the decrease being higher at pH 2.5 than at pH 7.5. Condensed tannins from each Leucaena species were also separated by size exclusion chromatography, and the fractions examined for protein-precipitating capacity. In general, it was found that the larger-sized condensed tannin of the accessions L pallida and L trichandra could precipitate more protein than the smaller-sized condensed tannin. This pattern was not found for L leucocephala. (C) 2001 Society of Chemical Industry.

Mining wheat germplasm collections for yield enhancing traits

The material in genebanks includes valuable traditional varieties and landraces, non-domesticated species, advanced and obsolete cultivars, breeding lines and genetic stock. It is the wide variety of potentially useful genetic diversity that makes collections valuable. While most of the yield increases to date have resulted from manipulation of a few major traits (such as height, photoperiodism, and vernalization), meeting future demand for increased yields will require exploitation of novel genetic resources. Many traits have been reported to have potential to enhance yield, and high expression of these can be found in germplasm collections. To boost yield in irrigated situations, spike fertility must be improved simultaneously with photosynthetic capacity. CIMMYT's Wheat Genetic Resources program has identified a source of multi-ovary florets, with up to 6 kernels per floret. Lines from landrace collections have been identified that have very high chlorophyll concentration, which may increase leaf photosynthetic rate. High chlorophyll concentration and high stomatal conductance are associated with heat tolerance. Recent studies, through augmented use of seed multiplication nurseries, identified high expression of these traits in bank accessions, and both traits were heritable. Searches are underway for drought tolerance traits related to remobilization of stem fructans, awn photosynthesis, osmotic adjustment, and pubescence. Genetic diversity from wild relatives through the production of synthetic wheats has produced novel genetic diversity.

Analysis of genetic diversity in Cassia brewsteri with randomly amplified DNA fingerprints (RAFS)

Genetic diversity in Cassia brewsteri (F. Muell.) F. Muell. ex Benth. was assessed with Randomly Amplified DNA Fingerprints (RAFs). Thirty accessions of C. brewsteri collected from throughout its natural distribution were analysed with three random decamer primers, along with three accessions of C. tomentella (Benth.) Domin and a single accession of each of C. queenslandica C. T. White and C. marksiana (F. M. Bailey) Domin. The three primers yielded a reproducible amplification profile of 265 scorable polymorphic fragments for the 35 accessions. These molecular markers were used to calculate Nei and Li similarity coefficients between each pair of individuals. A matrix of dissimilarity of each pair of individuals was examined by multidimensional scaling (MDS). The analysis supports the division of C. brewsteri into two subspecies and the suggestion that intergradation of C. brewsteri and C. tomentella can occur where the distributions of these species meet.

An embryo-rescue protocol for Vigna interspecific hybrids

A successful embryo-rescue and culture protocol was developed for use with several indigenous Vigna species and mungbean cultivars grown in Australia. Germination of Vigna immature embryos and their subsequent development into plants was influenced by the time at which the embryos were isolated and by which medium additives were placed in the embryo-rescue medium. A medium containing MS basal nutrients with sucrose (88 mM), casein hydrolysate (500 mg L-1) and agar (8 g L-1) but devoid of plant-growth regulators was found to be the best for germination of immature embryos for all four Vigna species investigated. The protocol for successful germination of non-hybrid immature embryos was applied to the recovery of interspecific hybrids involving mungbean and five native Vigna species that had previously been found difficult to hybridise. Several putative hybrid plants were obtained including a confirmed interspecific cross between V. luteola (Jacq.) Benth and V. marina (Burm.) Merrill.

Patterns of resistance to angular leaf spot, anthracnose and common bacterial blight in common bean germplasm

Diseases and insect pests are major causes of low yields of common bean (Phaseolus vulgaris L.) in Latin America and Africa. Anthracnose, angular leaf spot and common bacterial blight are widespread foliar diseases of common bean that also infect pods and seeds. One thousand and eighty-two accessions from a common bean core collection from the primary centres of origin were investigated for reaction to these three diseases. Angular leaf spot and common bacterial blight were evaluated in the field at Santander de Quilichao, Colombia, and anthracnose was evaluated in a screenhouse in Popayan, Colombia. By using the 15-group level from a hierarchical clustering procedure, it was found that 7 groups were formed with mainly Andean common bean accessions (Andean gene pool), 7 groups with mainly Middle American accessions (Middle American gene pool), while 1 group contained mixed accessions. Consistent with the theory of co-evolution, it was generally observed that accessions from the Andean gene pool were resistant to Middle American pathogen isolates causing anthracnoxe, while the Middle American accessions were resistant to pathogen isolates from the Andes. Different combinations of resistance patterns were found, and breeders can use this information to select a specific group of accessions on the basis of their need.

Genetic variability in cultivated common bean beyond the two major gene pools

It is generally accepted that two major gene pools exist in cultivated common bean (Phaseolus vulgaris L.), a Middle American and an Andean one. Some evidence, based on unique phaseolin morphotypes and AFLP analysis, suggests that at least one more gene pool exists in cultivated common bean. To investigate this hypothesis, 1072 accessions from a common bean core collection from the primary centres of origin, held at CIAT, were investigated. Various agronomic and morphological attributes (14 categorical and 11 quantitative) were measured. Multivariate analyses, consisting of homogeneity analysis and clustering for categorical data, clustering and ordination techniques for quantitative data and nonlinear principal component analysis for mixed data, were undertaken. The results of most analyses supported the existence of the two major gene pools. However, the analysis of categorical data of protein types showed an additional minor gene pool. The minor gene pool is designated North Andean and includes phaseolin types CH, S and T; lectin types 312, Pr, B and K; and mostly A5, A6 and A4 types alpha-amylase inhibitor. Analysis of the combined categorical data of protein types and some plant categorical data also suggested that some other germplasm with C type phaseolin are distinguished from the major gene pools.

Osmoregulative capacity in birdseed millet under conditions of water stress. I. Variation in Setaria italica and Panicum miliaceum

Experiments involving 14 accessions of Panicum miliaceum L. (Proso millet) and 11 accessions of Setaria italica L. (Foxtail millet) have demonstrated variability in the degree of osmoregulative capacity among these accessions. Birdseed millet is generally claimed to be sensitive to drought stress, apparently because of a shallow root system. Accessions with high osmoregulative capacity demonstrate at least some drought tolerance. Osmoregulative capacity was measured on flag leaves of headed millet plants in pots undergoing water stress in a controlled environment chamber. Osmoregulative capacity was determined from the relationship between osmotic potential and leaf water potential; and the logarithmic relationship between osmotic potential and relative water content. The group of accessions of S. italica showed an overall level of osmoregulative capacity which was greater than that observed for the group of P. miliaceum accessions. Four accessions of S. italica (108042, 108463, 108541 and 108564) and one accession of P. miliaceum (108104) demonstrated high osmoregulative capacity. Differences of 1.05 MPa or more between observed and estimated osmotic potential were found at relative water contents of 80 % among these accessions. The extent of osmoregulative capacity was associated with osmotic potential at full turgor and the rate of decline in osmotic potential as leaf water potentail declined.