Enteropathogenic Escherichia coli (EPEC) is one of the etiological agents that causes diarrhea in weaning pigs. In this study, we report that mutating both relA and spoT genes in EPEC E2348/69 can promote bacterial clearance in porcine gastrointestinal tract (GIT). Our experimental analyses showed that an E2348/69 ΔrelAΔspoT mutant strain was not detected in porcine feces after 1 day post-infection (dpi), whereas its parental strain was continuously detected in porcine feces within 10 dpi. Histologic assessment revealed that the mutant strain was unable to induce moderate pathologic lesions in porcine GIT when compared to those with the wildtype strain. Taken together, our data suggest that the relA and spoT genes in EPEC play an important role in bacterial survival and pathogenesis in porcine GIT.

역병(Phytophthora capsici)과 세균성점무늬병(Xanthomonas euvesicatoria)에 복합저항성인 핵유전형 웅성불임계(Genic male sterile line, GMS)를 육성하기 위하여 역병 저항성 핵유전형 웅성불임계에 역병-세균성점무늬병 복합저항성 계통을 교배하여 작성한 조합의 와 세대에 대하여 두 가지 병에 대한 저항성 선발을 실시하였다. 역병 저항성은 잘 알려져 있는 KC294(CM334)와 KC263(AC2258)에서 도입하고, 세균성점무늬병 저항성은 KC47(PI24467)에서 도입되었다. 역병에 고도의 저항성을 지닌 GMS 계통이 얻어졌으며, 이들은 세균성점무늬병에도 양적으로 저항성을 나타낼 것으로 기대된다.

감미종 고추에 더뎅이병(病)에 대한 저항성(抵抗性)을 도입하기 위하여 품질이 우수하면서 국내 적응성이 뛰어난 피만계 품종 Keystone Resistant Giant #3과 더뎅이병에 저항성인 PI271322를 교배하여 그 후대의 유전적 분리 양상을 조사한 결과 더뎅이병균 race 1에 대하여는 저항성(抵抗性)이 과민형반응(過敏型反應)으로 나타났으며 여기에는 한개의 우성유전자가 관여하는 것으로 밝혀졌다. race 3에 대해서는 발병정도가 연속적(連續的) 변이(變異)를 나타내어 저항성은 양적유전(量的遺傳)을 하는 것으로 나타났다. 집단에서 비과민형반응을 나타내는 개체간의 race 1에 대한 발병지수(發病指數)와 race 3에 대한 발병지수 간에는 고도(高度)의 상관관계(相關關係)가 있는 것으로 나타나 PI271322에 들어 있는 비과민형의 일반저항성 성분은 race에 비특이적으로 작용하는 것으로 나타났다. 따라서 에서 race 1에 과민형반응을 나타내고 race 3에 저항성인 개체를 선발하여 여교잡(戾交雜)육종을 계속할 수 있었다.

역병에 저항성인 PI201232와 더뎅이병 저항성인 PI271322와 PI163192를 교배하여 각 병해에 대한 저항성과 두가지 병해 저항성간의 유전적 관계를 검토하였다. 더뎅이병균 race 3에 대한 PI271322의 비과민반응형 저항성은 양적으로 유전하였다. PI201232의 역병에 대한 저항성은 2개의 우성유전자에 가까운 양식으로 유전하였다. PI271322의 더뎅이병균 race 1에 대한 과민반응형 저항성은 한개의 우성유전자 양식으로 유전하였다. PI163192는 더뎅이병균 race에 비특이적으로 저항성이었으며 우성효과가 큰 양적유전 양식으로 유전하였다. 더뎅이병균에 대한 저항성은 역병에 대한 저항성과는 독립적으로 유전하였다.

Bacterial spot of tomato is a disease complex caused by at least four species of Xanthomonas and leads to severe yield and quality losses in humid growing conditions in the world. Five physiological species (T1-T5) have been defined by their virulence on tomato varieties. These races are associated with three species: X. euvesicatoria (T1), X. vesicatoria (T2), and X. perforans (T3-T5). Recent epidemics of X. gardneri has occurred in the Midwest United States. In this study, we developed germplasm with resistance to multiple species of bacterial spot. Six advanced breeding lines with at least three different source of resistance were crossed and their F1 hybrids were inter-mated to produce a complex breeding population consisting over 1,100 progeny. Three lines (OH7663, OH7667 and 2k7-6117-S2) were selected by field evaluations of the population against T1, T2, T3, and X. gardneri. Graphical genotypes demonstrated that these breeding lines contain a QTL and Rx-4/Xv3 in coupling phase on chromosome 11 as well as Rx-3 on chromosome 5. In order to test the combining ability of the lines, we developed hybrids from multiple crosses and conducted replicated field trials to evaluate bacterial spot resistance and yield. As a male parent, OH7663 showed acceptable combining ability for yield and for resistance against multiple species of Xanthomonas. Several hybrids produced yields that were not significantly different from yields of commercial varieties.

Bacterial spot of tomato (Solanum lycopersicum L.) is caused by at least four species of Xanthomonas with multiple physiological races. In this study, we developed a mapping population for association analysis of bacterial spot resistance. For this population, six advanced breeding lines with distinct sources of resistance were first crossed in all combinations and their F1 hybrids were intercrossed. The 1,100 segregating progeny from these crosses were evaluated in the field against T1 strains. Based on this individual evaluation, we selected 5% of the most resistant and 5% of the most susceptible progeny for evaluation as plots in two subsequent replicate field trials inoculated with T1 and T3 strains. A total of 461 markers across 12 chromosomes were used for genotyping these selections. Of these markers, an optimized subset of 384 SNPs was derived from the 7,720 SNP Infinium array developed by the Solanaceae Coordinated Agricultural Project (SolCAP). For association analysis to detect known resistance loci and additional novel loci, we used the mixed models with correction for population structure, and found that accounting for kinship appeared to be sufficient. Detection of known loci was not improved by adding a correction for structure using either a Q matrix from model-based clustering or covariate matrix from Principal Component Analysis. Both single-point and haplotype analyses identified strong associations in the region of the genome known to carry Rx-3 (chromosome 5) and Rx-4/Xv3 (chromosome 11). Additional QTL associated with resistance were detected on chromosomes 1, 3, 4, 6 and 7 for T1 resistance and chromosomes 2, 4, and 6 for T3 resistance. Haplotype analysis improved our ability to trace the origin of positive alleles. These results demonstrate that both known and novel associations can be identified using complex breeding populations that have experienced directional selection.