Hybrid 'Sinta' papaya exhibits unique ACC synthase 1 cDNA isoforms

Five ripening-related ACC synthase cDNA isoforms were cloned from 80% ripe papaya cv. 'Sinta' by reverse transcription-PCR using gene-specific primers. Clone 2 had the longest transcript and contained all common exons and three alternative exons. Clones 3 and 4 contained common exons and one alternative exon each, while clone 1, the most common transcript, contained only the common exons. Clone 5 could be due to cloning artifacts and might not be a unique cDNA fragment. Thus, there are only four isoforms of ACC synthase mRNA. Southern blot analysis indicates that all five clones came from only one gene existing as a single copy in the 'Sinta' papaya genome. Multiple sequence alignment indicates that the four isoforms arise from a single gene, possibly through alternative splicing mechanisms. All the putative alternative exons were present at the 5'-end of the gene comprising the N-terminal region of the protein. 'Sinta' ACC synthase cDNAs were of the capacs 1 type and are most closely related to a 1.4 kb capacs 1-type DNA (AJ277160) from Eksotika papaya. No capacs 2-type cDNAs were cloned from 'Sinta' by RT-PCR. This is the first report of possible alternative splicing mechanism in ripening-related ACC synthase genes in hybrid papaya, possibly to modulate or fine-tune gene expression relevant to fruit ripening.

Assessment of P availability in heavily fertilized soils using the diffusive gradient in thin films (DGT) technique

Phosphorus-availability tests typically provide an indication of quantity of P available (Colwell bicarbonate-extractable P), or of the intensity of supply (0.01 M CaCl2-extractable P). The soil's capacity to buffer P is more difficult to assess, and is generally estimated using a P-adsorption curve. The diffusive gradient in thin films (DGT) approach may provide a simpler means of assessing a soil's ability to maintain soil solution P. Optimal extraction conditions were found to be 24 h exposure of DGT samplers to saturated soil. The DGT approach was evaluated on a range of 24 soils, some of which had high Colwell- (>100 mu g g(-1)) and Bray 1- (>30 mu g g(-1)) extractable P content, but showed a tomato (Lycopersicon esculentum Mill.) yield response to the addition of P fertilizer. The DGT approach provided an excellent separation of soils on which tomato showed a yield response, from those where fertilizer P did not increase dry-matter yield. Phosphorus accumulation was strongly correlated with soil solution P concentration and anion exchange resin-extractable P, but showed poor correlation with Colwell- or Bray 1-extractable P. The DGT P accumulation rate of 3.62 x 10(-7) to 4.79 x 10(-5) mol s(-1) m(-3) for the soils tested was comparable to the uptake rate of roots of tomato plants that were adequately supplied with P (2.25 x 10(-5) mol s(-1) m(-3)).

Identification and characterization of non-pathogenic Fusarium oxysporum capable of increasing and decreasing Fusarium wilt severity

Fusarium wilt of banana is a potentially devastating disease throughout the world. Options for control of the causal organism, Fusarium oxysporum f.sp. cubense (Foc) are limited. Suppressive soil sites have previously been identified where, despite the presence of Foc, Fusarium wilt does not develop. In order to understand some aspects of this disease suppression, endophytic Fusarium oxysporum isolates were obtained from banana roots. These isolates were genetically characterized and compared with an isolate of Fusarium oxysporum previously identified as being capable of suppressing Fusarium wilt of banana in glasshouse trials. Three additional isolates were selected for glasshouse trials to assess suppression of Fusarium wilt in two different cultivars of banana, Cavendish and Lady Finger. One isolate (BRIP 29089) was identified as a potential biocontrol organism, reducing the disease severity of Fusarium wilt in Lady Finger and Cavendish cultivars. Interestingly, one isolate (BRIP 45952) increased Fusarium wilt disease severity on Cavendish. The implications of an isolate of Fusarium oxysporum, non-pathogenic on banana, increasing disease severity and the potential role of non-pathogenic isolates of Fusarium oxysporum in disease complexes are discussed. (c) 2006 Published by Elsevier Ltd on behalf of The British Mycological Society.

Acibenzolar-S-methyl and methyl jasmonate treatments of glasshouse-grown freesias suppress post-harvest petal specking caused by Botrytis cinerea

Compounds that activate host plant defence responses potentially offer socio-environmentally sound alternative methods for disease control. In a series of glasshouse trials over 2 years, pre-harvest sprays with acibenzolar-S-methyl (ASM) and methyl jasmonate (MeJA) were tested for suppression of post-harvest infection of cut Freesia hybrida L. flowers by Botrytis cinerea. For the ASM treatments, variability in reducing the incidence of B. cinerea disease was observed between years freesia varieties, incubation temperatures and ASM concentrations. In the first year, the greatest reductions in lesion numbers on ASM-treated var. 'Cote d'Azur' were recorded using 2.86 mM ASM. For three different post-harvest temperature regimes, the relative reductions in lesion numbers, compared to untreated controls, were 45% at 5 degrees C, 40% at 12 degrees C and 30% at 20 degrees C, respectively. In the second year, lesion numbers were most reduced using 1.43 mM ASM to treat freesia var. 'Dukaat' flowers. Here, the relative reductions were to 44% at 5 degrees C, 26% at 12 degrees C and 51% at 20 degrees C. MeJA treatments were, in general, more consistently effective than ASM treatments in reducing lesion numbers and lesion diameters on cut freesia flowers. MeJA-treated (0.2 mM) freesia flowers (var. 'Dukaat') incubated at 20 degrees C showed relative reductions of 62%, and 45% for lesion number and lesion diameter, respectively. The differing efficacy between ASM and MeJA treatments could be attributed to their differential abilities to induce the salicylic acid (SA)-mediated vs. the jasmonic acid (JA)-mediated host defence pathways, respectively.