Quantitative resistance of Phaseolus vulgaris to common bacterial blight: sources, inheritance and genomic association

• Ano de defesa: 2019
• Autor(a) principal: Monteiro, Ana Leticia Rocha
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa; Fitopatologia
• Palavras-chave em Português: Feijão - Doenças e pragas; Xanthomonas axonopodis pv. phaseoli; Resistência genética; Fitopatologia
• Link de acesso: https://locus.ufv.br//handle/123456789/30082

Common Bacterial Blight (CBB), caused by the Gram-negative bacterium Xanthomonas axonopodis pv. phaseoli (Xap) is one of the major diseases that affect common bean production worldwide. To understand diverse aspects of the mechanisms behind resistance of common bean to CBB, this study first (Chapter 1) demonstrated that the use of scissors and multiple needle inoculation methods, that introduce the bacterium directly into the intercellular spaces, result in disease symptoms considered more severe than spray inoculation and, because it resembles natural infection, the latter was chosen to conduct further experiments. Of nine genotypes tested, BRS Radiante and IAPAR 16 exhibited high resistance against seven Xap isolates from different origins. The resistance of these varieties was associated with restriction of bacterial multiplication in planta and was not necessarily related to stomatal density. In the second step (Chapter 2), hybrids of genotype combinations in a partial diallel scheme (3 x 5) were generated to identify the most promising for resistance to CBB, based on estimates of general combining ability (GCA) and specific combining ability (SCA). Because of the lack of reliable morphological markers to distinguish hybrids from parents for several of these combinations, a toolkit of SCAR (Sequence Characterized Amplified Region) markers was assembled. Based on GCA values, it was concluded that variety BRS Radiante greatly contributes to enhance common bean resistance to CBB whereas nine hybrid combinations were shown to be promising to increase resistance to CBB according to SCA values. Then, hypotheses for resistance inheritance in the BRS Radiante × Carioca MG combination were tested by chi-square statistics. The resistance inheritance of BRS Radiante to CBB was best explained by a 9:7 ratio, suggesting that it is conditioned by two complementary dominant genes. In addition, a maximum likelihood analysis indicated the effect of a main dominant gene with additive effect and polygenes involved in CBB resistance. In the third step (Chapter 3) of this work, BC 1 F 1 and BC 2 F 1 plants derived from the combination BRS Radiante (parental donor) × Carioca MG (recurrent parent) were obtained. The backcrossed plants obtained were genotyped with SCAR markers and phenotyped for resistance to CBB. Two BC 1 F 1 and BC 2 F 1 plants were highly resistant to CBB, indicating that they are excellent candidates to advance them to the next generations. Finally (Chapter 4), it was aimed to classify 103 common bean varieties for resistance to CBB based on disease severity and area under the disease progress curve (AUDPC). Twenty-nine varieties with high levels of horizontal resistance to CBB associated with lower AUDPC values were identified. Then, an exploratory Genome- Wide Association Study (GWAS) was conducted with 80 of these varieties using 384 Single Nucleotide Polymorphism (SNP) markers. Genes coding for proteins whose putative functions have previously been associated with plant resistance to diseases, such as serine/threonine kinases, glutamine synthetases, lectin-domain proteins, among others, were identified. The main contributions of this study to the scientific community are: knowledge on common bean genotypes highly resistant to CBB; knowledge on generation of genotype combinations appropriate to obtain resistance against CBB; biological material useful to undertake studies on the genetic and molecular mechanisms underlying common bean resistance against CBB; candidate genes that may be involved in the resistance response of common bean to Xap; and molecular tools useful in the identification of common bean hybrid plants. The knowledge and biological material generated in this work set the stage for additional studies on the common bean-X. axonopodis pv. phaseoli interaction.