The combination of plant density, fungicide, and levels of genotype resistance to white mold (WM) has not been studied for the role played in affecting performance of common bean with type III growth habit under WM pressure. We established four sprinkler-irrigated trials in the fall-winter season in Brazil, combining density (8, 14, 20 or 26 plants/m2), genotype (susceptible or partially resistant to WM), and fungicide to manage WM (two fluazinam applications or without fluazinam) at 0.5 m row spacing in fields infested with sclerotia. One trial was established in a warm region, aiming to obtain low WM pressure. For three trials, the linear mixed model was used. WM pressure in the trials ranged from low to high. Genotype × density × fungicide and genotype × density interactions were not significant for incidence, severity, and yield for all trials. In the three trials, severity was 29% lower at 8 than at 26 plants/m2, and yield at 14 plants/m2 (3,294 kg/ha) was 14% higher than yield at 8 plants/m2 (P = 0.035) where fluazinam was applied. However, without fluazinam, density did not affect yield. In conclusion, plant density for type III bean cultivars does not need to take into account their resistance levels to WM in the fall-winter season. However, fungicide treatment to manage WM affects the decision on density, with 8 to 12 plants/m2 recommended if fungicide is not an option to manage WM (as in organic systems), and 10 to 14 plants/m2 recommended if fungicide applications are likely.
BRSMG Camaleão' is a mungbean cultivar with large, shiny, green seeds released for the state of Minas Gerais, Brazil. It was developed by the Asian Vegetable Research and Development Center as line VC 6148-B-16. In seven trials established in the Zona da Mata region, it had an average yield of 1493 kg ha -1 and 1000-seed weight of 68-78 g.
Development of common bean cultivars with partial white mould resistance through breeding techniques has been a challenge in Brazil. As yet, lines/cultivars from breeding programmes have not been investigated for resistance; therefore, this study screened 107 lines/cultivars for their reactions to white mould in 14 preliminary trials conducted under irrigation. Thirteen resistant lines/cultivars (three of Andean origin) and six Mesoamerican cultivars (three intermediately resistant and three susceptible) were selected for further investigation. These lines/cultivars and the resistant control A195 were evaluated in six advanced trials and two straw tests to assess the effectiveness of the screening procedure. In 11 preliminary trials, screenings were performed under moderate/high or higher disease pressure. These pressures occurred in two advanced trials in which, when yields were averaged across moderate/high and high pressures, 10 Mesoamerican lines/cultivars selected for resistance yielded 14%, 23%, and 38% more than intermediately resistant cultivars, A195, and susceptible cultivars, with median disease ratings (1–9 scale) of 4.5, 5.7, 5.7, and 6.7, respectively. In the straw test, three Andean lines/cultivars (A195 included) and two susceptible cultivars in the field were among those with the highest levels of physiological resistance. Thus, field rating under high disease pressure and greenhouse rating did not correlate significantly, suggesting that field trials are critical to evaluating resistance and to identifying high‐yielding beans. Therefore, lines/cultivars from breeding programmes assessed in field trials may provide a low cost and fast way to identify high‐yielding bean cultivars with partial resistance to white mould in the subtropical southern hemisphere.
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.
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