Improving integrated management of white mold by using partial resistant genotype and adequate plant population in common bean

Abstract

Improving integrated management of white mold by using partial resistant genotype and adequate plant population in common bean. Adviser: José Eustáquio de Souza Carneiro. Co-adviser: Rogério Faria Vieira. The white mold (WM), caused by the soil fungus Sclerotinia sclerotiorum, is the main disease of common bean in the dry season in the Southeastern and Mid-western regions of Brazil. The integrated management by using partially resistant genotypes with adequate plant population may keep WM infection at low damage levels, thereby increasing yield. Studies showed that plant population for beans of type II growth habit could be higher than that currently recommended, but concerns with the possibility of increasing disease, especially WM, lead researchers to limit the plant population recommended. However, as partial resistant genotype of bean may be released soon, the use of high plant population could improve seed yield without a great increase on WM incidence and severity. We conducted two studies. In the first, we reevaluated the strategy of field selections/evaluations in obtaining high-yield genotypes with partial resistance to WM. In the second, we evaluated to the performance of type II bean partially resistant to WM in the field using high plant population in areas infested with sclerotia of S. sclerotiorum. In the first study, we assessed four groups (G) of Mesoamerican genotypes and a group of early maturing Andean genotypes (resistant control): G1 = seven genotypes with resistance; G2 = four elite lines with putative resistance; G3 = A195, G122, Cornell 605, and Ouro Branco (Andean), G4 = two cultivars with intermediate resistance, and G5 = three susceptible cultivars. Genotypes of G2 were screened in the 2013- 2014 VCU trials; the others, in the 2008-2011 VCU trials. A linear mixed model was used. To evaluate the performance of the type II bean with partial resistant to WM under high plant population, we combined between-row spacing levels (0.25 or 0.50 m) with in-row plant density levels (7, 10, 13 or 16 plants m -1 ). The effects of these factors on WM infection and yield were assessed using the carioca line CNFC 10720, which has partial resistance to WM. In the first study, the contrast G1,G2 vs. G3 was non-significant for WM incidence and severity index, indicating that genotypes selected for partial resistant were as resistant as the control group. Additionally, G1,G2 yielded 43% more (p < 0.001) and produced 33% less sclerotia (p = 0.001) than G3. In the second study, yield at 0.25 m was 28% higher than yield at 0.50 m (p < 0.001). The use of 13 plants m -1 provided the higher yield for both 0.25 and 0.50 m. In conclusion, the first study supports the previous findings and add new evidencethat support the effectiveness of the strategy proposed to identify resistance for WM associated with high yield for the dry season in Brazil. The results related to the type II bean with partially resistant to WM indicate that plant population higher than that currently recommended may improve seed yield. However, further studies of plant population are needed under condition of diseases pressure, especially WM, before a conclusion can be reached. Keywords: Sclerotinia sclerotiorum. Phaseolus vulgaris. Genetic resistance. Plant population. Dry bean. Escape mechanisms.