Bacterial panicle blight (BPB) is among the three most limiting rice diseases in Louisiana and the southern United States. The identity and characterization of pathogens associated with this disease was unclear. This research details studies carried out on the pathogens causing BPB on rice in Louisiana and other rice producing southern states. Bacterial strains were isolated from BPB-infected sheath, panicle, or grain samples collected from rice fields in Louisiana, Arkansas, Texas, and Mississippi. In greenhouse inoculation tests, 292 of 364 strains were pathogenic on rice seedlings or panicles. Identification of strains in the pathogen complex by growth on S-PG medium, carbon source utilization profile (Biolog), cellular fatty acid analysis, and polymerase chain reaction (PCR) methods revealed that 76 and 5% of the strains were Burkholderia glumae and B. gladioli, respectively. The other strains have not been conclusively identified. Although strains of both species produced similar symptoms on rice, B. glumae strains were generally more aggressive and caused more severe symptoms on rice than B. gladioli. Virulent strains of both species produced toxoflavin in culture. The two species had similar growth responses to temperature, and optima ranged from 38 to 40°C for B. glumae and 35 to 37°C for B. gladioli. PCR was the most sensitive and accurate method tested for identifying the bacterial pathogens to the species level. The 16S rDNA gene and 16S-23S rDNA internal transcribed spacer (ITS) region sequences of the B. glumae and B. gladioli strains from rice showed more than 99% sequence homology with published sequences. A real-time PCR system was developed to detect and quantify this pathogen from infected seed lots. Our results clearly indicate that B. glumae and B. gladioli were the major pathogens causing BPB in the southern United States.

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Panicle blight of rice (Oryza sativa), caused by the bacterium Burkholderia glumae, is one of the most important new diseases in rice production areas of the southern United States. In this study, pathogenic strains were isolated from diseased panicles in Arkansas rice fields and examined using the Biolog GN microplate system, whole cell fatty acid methyl ester analysis (FAME), rep-polymerase chain reaction (PCR) genomic DNA fingerprinting, and 16S–23S ribosomal DNA (rDNA) intergenic transcribed spacer (ITS) sequence analysis. The B. glumae isolates from Arkansas can be divided into two major groups, but their genetic diversity was relatively low as revealed by 16S–23S rDNA ITS sequence analysis. Since no practical method existed, up to now, for testing the presence of B. glumae in rice seeds, we have developed in this study a real-time PCR method that is effective in detecting and identifying the pathogen in seed lots and in whole plants. The specific PCR primers were designed based on the 16S–23S rDNA ITS sequence of several representative isolates from Arkansas and Japan. This method is highly sensitive, rapid, and reliable, and has great potential for analyzing large numbers of samples without the need for DNA extraction or agarose gel electrophoresis. Although vertical resistance has not been observed among tested rice cultivars, LM-1 and Drew exhibited considerable resistance to B. glumae infection based on disease lesion size and the bacterial growth in planta.

We recently identified a positional candidate for the XRCC2 DNA repair gene at human chromosome 7q36.1. We have now cloned the cDNA for this gene from both human and mouse and show that it is a highly conserved novel member of the recA / RAD51 recombination repair gene family. The cDNA is able to complement significantly the phenotype of a unique cell line, irs1 , which shows extreme sensitivity to DNA cross-linking agents and genetic instability. Thisphenotype is consistent with a role for the XRCC2 gene in recombination repair in somatic cells, suggesting that in addition to RAD51 , other members of this gene family have an important function in high fidelity repair processes in mammals. Despite this function, the XRCC2 gene transcript is expressed at a very low level in somatic tissue, but is elevated in mouse testis, suggesting an additional role in meiosis.

Grapevine trunk diseases are a major concern to the wine-and table-grape industries worldwide, limiting both vineyard longevity and productivity. Field surveys conducted throughout the grape-growing regions of Arkansas and Missouri revealed the presence of three economically important grapevine trunk diseases including, Botryosphaeria canker, Eutypa dieback and esca. Morphological studies along with multi-gene phylogenetical analyses confirmed the identification of 15 different fungal taxa associated with different vascular symptoms. These include Botryosphaeria dothidea, Diatrypella sp.