Summary Limited information is available regarding the susceptibility or resistance of soybean cultivars to Meloidogyne enterolobii. Recently, a new race of this species was detected in Brazil parasitising cotton and soybean. This nematode has the potential to pose a problem in both of these crops, since it is pathogenic and virulent to several economically important plants that have resistance genes to other Meloidogyne species. The aim of this study was to assess the responses of EMBRAPA’s main soybean cultivars with confirmed resistance to M. incognita and M. javanica to the two races of M. enterolobii detected in Brazil. Additionally, this study aimed to characterise the aggressiveness of these nematode races. The experiments were conducted in a plastic house, in a factorial scheme with 16 soybean cultivars × two M. enterolobii races (guava and cotton), totalling 32 treatments × eight replications, and evaluated with two replications over time. Soybean sowing took place in pots containing 1.7 l of a mixture of soil, sand and Bioplant® substrate (1:1:1), previously autoclaved. Each soybean plant was inoculated with 5000 eggs of M. enterolobii. After 75 days for the first experiment, and 90 days for the second, the following variables were evaluated: gall index (GI), egg mass index (EMI), total number of eggs per g root (NEGR) and the reproduction factor (RF). Both races of M. enterolobii showed reproductive ability in all soybean genotypes (with or without known genetic resistance), albeit with moderate to low values in comparison to their reproduction on tomato plants. The race from cotton was considered statistically more aggressive than the guava population on soybean cultivars. Only ‘BRS 7180 IPRO’ was moderately resistant to both races in both experiments. In view of the importance and prospects for expansion of the soybean crop, the findings of this study contribute to a better understanding of the resistance and aggressiveness exhibited by the two races of M. enterolobii, Moreover, the study highlights the significant challenge that lies ahead in developing breeding programmes to select soybean genotypes with multiple resistance to Meloidogyne spp.
Cowpea, Vigna unguiculata, is a legume adapted to regions with a tropical climate and limited water resources, and it has become a basic food source and income generator. Root-knot nematodes (Meloidogyne spp.) cause substantial damage to the root system, resulting in yield losses. Genetic resistance is one of the most efficient management methods. The objective of this study was to generate information on genetic resistance to Meloidogyne incognita and Meloidogyne javanica of Brazilian cowpea genotypes. For this, 18 accessions of cowpea from the collection of Embrapa Meio-Norte and six control accessions of cowpea were tested in completely randomized design with six replications, evaluated 60 days after inoculation, and carried out twice in time. To assess root penetration of nematodes and root gall formation in NIL-CB3isoline, which allows reproduction but limits gall formation, nematodes inside the roots were stained with acid fuchsin, after inoculation with 5000 J2, with estimates at 72 h time-points up to 28 days. None of the 18 accessions from Embrapa showed resistance to M. javanica, but accessions MNC06-895-1, MNC04-14, MNC06-909-6, 98, MNCO4-907-35, and Am60-15 showed resistance to M. incognita. There was a reduction in the number and size of galls in the NIL-CB3 egg isoline, and an increase in formation of males, which are not important for parasitism. Given the importance and prospects for expansion of the cowpea crop throughout Brazil, the results of this study contribute to the knowledge on the reaction of Brazilian cowpea genotypes to the root-knot nematode.
Background: Among the pathogens that reduce cotton productivity in Brazil, Meloidogyne incognita is one of the most important as it causes severe yield losses and is widespread. The most recommended methods for control of this species are the use of resistant cultivars and crop rotation systems. In Brazil, M. incognita races 3 and 4 have already been reported as cotton parasites but the race 3 is the most commonly found and widely disseminated.This work aimed at selecting virulent and aggressive populations of M. incognita race 3 for testing sources of resistance to this nematode in cotton genotypes.Results: The three isolates of M. incognita race 3 were important for screening of resistant cotton genotypes. The isolate from Umuarama was the most aggressive followed by Moreira Sales and Iporã. The genotypes CD 05-419, CD 05-945, CD 05-1087 and CD 05-1170 showed good performance against M. incognita race 3 in both greenhouse and field conditions.Conclusions: The cotton genotypes CD05-945, CD05-1170, CD05-1087 and CD05-419 will be selected for future work involving tests for resistance against other important cotton pathogens. Those genotypes can also be used as source of genes for resistance to nematodes in cotton breeding programs. The search for virulent and aggressive M. incognita isolates was very important when screening for resistance in cotton germplasm.
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