Donald E. Groth

Diversities in Virulence, Antifungal Activity, Pigmentation and DNA Fingerprint among Strains of Burkholderia glumae

Burkholderia glumae is the primary causal agent of bacterial panicle blight of rice. In this study, 11 naturally avirulent and nine virulent strains of B. glumae native to the southern United States were characterized in terms of virulence in rice and onion, toxofalvin production, antifungal activity, pigmentation and genomic structure. Virulence of B. glumae strains on rice panicles was highly correlated to virulence on onion bulb scales, suggesting that onion bulb can be a convenient alternative host system to efficiently determine the virulence of B. glumae strains. Production of toxoflavin, the phytotoxin that functions as a major virulence factor, was closely associated with the virulence phenotypes of B. glumae strains in rice. Some strains of B. glumae showed various levels of antifungal activity against Rhizoctonia solani, the causal agent of sheath blight, and pigmentation phenotypes on casamino acid-peptone-glucose (CPG) agar plates regardless of their virulence traits. Purple and yellow-green pigments were partially purified from a pigmenting strain of B. glumae, 411gr-6, and the purple pigment fraction showed a strong antifungal activity against Collectotrichum orbiculare. Genetic variations were detected among the B. glumae strains from DNA fingerprinting analyses by repetitive element sequence-based PCR (rep-PCR) for BOX-A1R-based repetitive extragenic palindromic (BOX) or enterobacterial repetitive intergenic consensus (ERIC) sequences of bacteria; and close genetic relatedness among virulent but pigment-deficient strains were revealed by clustering analyses of DNA fingerprints from BOX-and ERIC-PCR.

Biological Control Activities of Rice-Associated Bacillus sp. Strains against Sheath Blight and Bacterial Panicle Blight of Rice

Potential biological control agents for two major rice diseases, sheath blight and bacterial panicle blight, were isolated from rice plants in this study. Rice-associated bacteria (RABs) isolated from rice plants grown in the field were tested for their antagonistic activities against the rice pathogens, Rhizoctonia solani and Burkholderia glumae, which cause sheath blight and bacterial panicle blight, respectively. Twenty-nine RABs were initially screened based on their antagonistic activities against both R. solani and B. glumae. In follow-up retests, 26 RABs of the 29 RABs were confirmed to have antimicrobial activities, but the rest three RABs did not reproduce any observable antagonistic activity against R. solani or B. glumae. According to16S rDNA sequence identity, 12 of the 26 antagonistic RABs were closest to Bacillus amyloliquefaciens, while seven RABs were to B. methylotrophicus and B, subtilis, respectively. The 16S rDNA sequences of the three non-antagonistic RABs were closest to Lysinibacillus sphaericus (RAB1 and RAB12) and Lysinibacillus macroides (RAB5). The five selected RABs showing highest antimicrobial activities (RAB6, RAB9, RAB16, RAB17S, and RAB18) were closest to B. amyloliquefaciens in DNA sequence of 16S rDNA and gyrB, but to B. subtilis in that of recA. These RABs were observed to inhibit the sclerotial germination of R. solani on potato dextrose agar and the lesion development on detached rice leaves by artificial inoculation of R. solani. These antagonistic RABs also significantly suppressed the disease development of sheath blight and bacterial panicle blight in a field condition, suggesting that they can be potential biological control agents for these rice diseases. However, these antagonistic RABs showed diminished disease suppression activities in the repeated field trial conducted in the following year probably due to their reduced antagonistic activities to the pathogens during the long-term storage in -70C, suggesting that development of proper storage methods to maintain antagonistic activity is as crucial as identification of new biological control agents.

Transgene Transfer to United States Commercial Rice Cultivars via Conventional Breeding Techniques

Abstract Breeding programs can benefit from transfer of a foreign gene from one transgenic plant to commercial cultivars through continuous backcrossing, especially to cultivars in which it is difficult to transfer a foreign gene directly through biotechnology. In this study, two homogeneous transgenic plants, T-28 and T-64 (from Taipei 309), and one homogeneous transgenic plant, N-84 (from Nipponbare), were used as donors of Bar gene. Commercial cultivars, Cypress and Laffite, were used as the recurrent parents. Three to five backcrosses were made using the transgenic plants as donor parents and the commercial cultivars as recurrent parent. The results from selected progeny rows, and two-years of yield tests with selected lines, indicated that the target Bar gene could be transferred to lines from homozygous transformants in 2–3 years of backcrossing, giving lines similar to the recurrent parents in phenotype and yield potential.

Visual Estimation of Rice (Oryza sativa L.) Grain Yield in Multiple Environments in Louisiana

Development of high-yielding rice (Oryza sativa L.) cultivars is a primary objective of most rice-breeding programs, and breeding progress is generally measured through increases in grain yield attributable to new cultivars. The pedigree-breeding method, commonly employed in rice-breeding programs, usually results in a large number of lines being discarded in early generations on the basis of visual estimates of grain yield potential. The objective of this research, conducted at five locations in 2007 and 2008 in Louisiana, was to evaluate the effectiveness of visual grain-yield predictions by two rice breeders. A second objective was to determine the effect of disease and lodging on the accuracy of visual selection. Across all years and locations, the grain yield estimates of both breeders were positively correlated with observed grain yield, indicating that visual selection for grain yield can be effective. Differences existed in the predictive ability of the breeders to estimate grain yield at different environments. Generally, breeders were more accurate in visually estimating grain yield when the standard deviation of the estimates was high, indicating that perceived phenotypic expression of grain yield is an important factor affecting the visual estimation of yield potential. Locations with high disease pressure and lodging resulted in a greater standard deviation of the yield estimates and improved the accuracy of visual estimation of grain yield.

Allelic Analysis for bar Gene from Different Rice Transformation Events

Abstract Mechanism(s) of gene transformation and integration in rice (Oryza sauva L.) is/are not currently well understood. This research was conducted to determine whether a transgene is inserted into the rice genome specifically or randomly. Seven homozygous transgenic Taipei (T) 309 and Nipponbare plants with the bar transgene from different rice transformation events were crossed. The segregation of F2 and F3 populations from a total of 21 crosses was studied in a greenhouse and field to determine if the genes were allelic or non-allelic. Five genomic locations appeared to be involved among the seven transgenic plants. An additional 20 homozygous transgenic T309 plants, with the bar transgene from different transformation events, were crossed reciprocally with the previous seven plants. One hundred and fifteen crosses made during 1999 and 2000 were analyzed for allelism. In some combinations, the genes were allelic, but most of them were non-allelic, with two or more pairs of genes being expressed. Twenty loci among the 27 transgenic plants were involved and some plants had several inserted genes expressed. Genes in nine out of 27 transformed plants were allelic. We concluded that the functional foreign (bar) gene was restrictively/preferentially inserted into the rice genome in some cases and was not completely randomly inserted and expressed in the rice genome. If the mechanism(s) for preferential insertion were identified, rice researchers could possibly control insertion sites of transgenes to optimize gene expression.