Twenty-five phenotypically and genotypically similar strains of a fastidious, xylem-limited bacterium were isolated from 10 plant disease sources including Pierce's disease of grapevines, phony disease of peach, periwinkle wilt, and leaf scorches of almond, plum, elm, sycamore, oak, and mulberry. The cells were single (occasionally filamentous), nonmotile, aflagellate straight rods (0.25 to 0.35 by 0.9 to 3.5 pm). They were gram negative, catalase positive, and oxidase negative, utilized hippurate, and produced gelatinase and often beta-lactamase but not beta-galactosidase, coagulase, lipase, amylase, phosphatase, indole, or HZS. The bacteria were strict aerobes with optimum growth at 26 to 28°C and pH 6.5 to 6.9 and had doubling times of 0.45 to 1.98 days in periwinkle wilt broth. Monoclonal antibodies prepared against the Pierce's disease bacterium reacted with all strains. DNA composition was 51 to 53 mol% guanine plus cytosine, and strains were at least 85% related in DNA hybridization. Sequencing of 16s ribosomal ribonucleic acid related them to the xanthomonads. These bacteria form a distinct group, and the name XyZeZZa fastidiosa is proposed, establishing a new genus with one species in the gamma subgroup of the eubacteria. Strain PCE-RR (ATCC 35879) is designated as the type strain. (13,16,26,27,33,36,37,41,44,45; J. Sherald, unpublished data).

Plants, when exposed to sub-lethal stress (induction stress), develop the ability to withstand severe temperatures and this phenomenon is often referred to as acquired thermotolerance. Earlier it was reported that induction stress alters gene expression and brings greater adaptation to heat stress and that the genetic variability in thermotolerance is only seen upon induction stress. Based on this concept, the temperature induction response (TIR) technique has been developed to identify thermotolerant lines. By following the TIR technique, sunflower hybrid KBSH-1 parents were screened for high temperature tolerance. Seedlings of parental lines including CMS 234 A, CMS 234 B and 6 D-1 showed considerable genetic variability for thermotolerance and it was attributed to the expression of existing residual variability for stress responses. Thus, the existing variability forms the basis for identifying thermotolerant lines. The identified parental inbred lines were selected and established in the field and crossed to get F1 hybrid seeds. The KBSH-1 hybrid developed from selected variants of parental lines was compared with the original KBSH-1 for thermotolerance. The selected KBSH-1 was more tolerant compared with the original hybrid both at the seedling as well as at the plant level. The physiological and molecular basis of thermotolerance was studied in the KBSH-1 original and the hybrid developed from selected variants of parental lines. The selected hybrid exhibited high tolerance to Menadione (naphthoquinone)-induced oxidative stress. Even the methyl viologen-induced oxidative stress damage was relatively less in the selected hybrid population. The selected hybrid also showed enhanced expression of the heat shock proteins HSP 90 and HSP 104 and also accumulated higher levels of the heat shock transcription factor HSFA.

Reduced spikelet fertility appears to be one of the major factors responsible for the decreased rice grain yield when cultivated under semi irrigated aerobic condition. We demonstrate that genotypes with better root systems coupled with higher cellular level tolerance (CLT) can significantly improve spikelet fertility under semi-irrigated aerobic condition in the field. A set of 20 contrasting rice accessions differing in root traits and CLT with significant molecular diversity were subjected to specific soil moisture regimes during a period between five days before and 10 days after anthesis. Lowest spikelet fertility was observed among the plants grown under water limited (WL) conditions followed by the plants grown aerobically in field conditions (AF). Deep rooted genotypes generally maintained higher spikelet fertility under both WL and AF conditions. Furthermore, genotypes that had high roots biomass as well as high CLT recorded the lowest reduction in spikelet fertility under WL and AF compared with the low root and low CLT genotype. This study emphasised the relevance of combining water acquisition and CLT for improving field level tolerance of rice to water limitation. Such genotypes recorded significantly higher grain yield under stress as well as well watered conditions. The study led to the identification of promising trait donor genotypes which can be exploited in breeding to develop superior trait pyramided cultivars suitable for semi irrigated aerobic cultivation.

Rickettsia-like bacteria associated with plum leaf scald and phony peach diseases were isolated from diseased but not from healthy tissues and cultured on charcoal-yeast extract medium (BCYE) buffered with ACES (2-[(2-amino-2-oxoethyl) amino]-ethanesulfonic acid). Optimum conditions for isolation and growth on BCYE medium were pH 6.5 to 6.9 at 20 and 25°C under normal atmosphere. Growth of primary colonies and first-passage subcultures was restricted, and colonies reached a maximum diameter of 0.6 mm in 60 days. After 12 passages, subcultures reached maximum growth in 21 days. The rickettsia-like bacteria from BCYE cultures were gram negative, serologically the same as those present in diseased peach and plum, and composed of rod-shaped cells measuring 0.35 by

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