The rice cultivar Baixiangzhan harbours a recessive gene xa42(t) determining resistance against Xanthomonas oryzae pv. oryzae

Bacterial leaf blight (BB) is among the “top 3” diseases in rice production. Breeding resistant cultivars has been the most effective strategy for BB management. The inbred cultivar Baixiangzhan (BXZ) showed a broad spectrum of resistance to five Xoo pathotypes in China, including the prevalent and highly virulent Xoo pathotypes Chinese Race V (CV), which can overcome the resistance of Xa4 and Xa21. The resistance heredity of BXZ has been explored in this study. A single recessive major resistance gene, which designated as xa42(t), confers resistance against the tested Xoo pathotypes CV. Linkage analysis lands xa42(t) on chromosome 6, and genetic mapping confines it to 3.9 cM region flanked by RM20558/RM20547 and RM20580. A further seven markers were developed from this interval for high‐resolution mapping, and the xa42(t) locus was narrowed to 34.8 Kb segment bounded by RM20572 and DT46. The only functionally predicted gene included in the target region is LOC_Os06g45960 if based on the ‘Nipponbare’ reference sequence. This candidate gene is predicted to encode a cytochrome P450 protein.     

Screening of wild Oryza species against bacterial leaf blight (Xanthomonas oryzae py. oryza) pathotypes of Punjab (India)

One-hundred and sixty-seven accessions belonging to 13 wild Oryza species were screened against the bacterial leaf blight (BB) pathogen (Xanthomonas oryzae pv. oryza) in Punjab, India. Nine species were identified as carrying resistant genes against the four most prevalent pathotypes under conditions in Punjab. These included O. barthii (eight accessions), O. longistaminata (five accessions), O. meridionalis (three accessions), O. nivara (five accessions), O. rufipogen (two accessions), and one accession each from O. punctata, O. minuta, O. malampuzhaensis and O. latifolia. This is the first report showing the availability of BB resistance in two species namely, O. meridionalis and O. punctata. The resistant accessions, especially those with a similar genome (AA) could potentially be used for the transfer of BB resistance to well-adapted high-yielding rice cultivars.     

Resistance to bacterial blight (Pseudomonas syringae pv. pisi) in Spanish pea (Pisum sativum) landraces

Pea bacterial blight (Pseudomonas syringae pv. pisi) has long been known to be present in pea growing areas of Spain and to cause serious crop losses, although there is no published record of its occurrence. A collection of 16 isolates from a winter pea trial in Valladolid in 1991 which were shown in this study to be P.s. pv. pisi races 4 and 6 would appear to be the first published record of the disease in Spain. This occurrence of races 4 and 6 is the same as reported for winter-sown peas in the South of France. Ten Pisum sativum landraces from different geographical areas of Spain and considered to be representative of the traditional pea crop, were tested for resistance to seven races of P.s. pv. pisi. Seedlings of each landrace were stem inoculated with the type strain of each race in a glasshouse. Resistance exhibited by the different landraces mainly conformed to those previously described in pea cultivars indicating various combinations of the main resistance genes: R3, R2+4, R3+4 and R2+3+4. R3 was the most frequent R gene, being present in all landraces. R4 was present in four and R2 in three of the landraces tested. Variation for resistance within landraces was limited except for landrace accessions ZP-0102, ZP-0109 and ZP-0137 which also showed variation for morphological traits. The resistance responses of landrace ZP-0109 were difficult to interpret, but suggested a genetic mixture with some evidence of less well documented R genes, R5 and/or R6, and possibly some unknown resistance to race 6. This revised version was published online in July 2006 with corrections to the Cover Date.