As the development of resistant cultivars can help in the management of stink bugs in soybeans, by helping to reduce the costs of insecticide applications and protect the longevity of the few molecules available for chemical control.
A soybean cultivation in the 2017/18 harvest exceeded 35 million hectares cultivated in Brazil and needs to maintain its grain productivity even under attack by diseases and insect pests. Among the main pests of soybeans, Stink bugs stand out for the damage caused directly to seeds still in filling phase until its maturation, when they insert their stylet into the seed and They secrete enzymes to facilitate their feeding. In addition to direct damage, also indirect ones occur, caused by pathogens that colonize the seeds in bite points. Among the most important bedbug species for soybeans, the brown stink bug euschistus heros, has stood out in recent harvests with high populations and at least potential damage to the crop, in addition to other species such as the small green stink bug Piezodorus guildinii, green-bellied stink bug Dichelops melacanthus and the green stink bug, nezara viridula that make up the grain-sucking insect complex.
In crops severely attacked by these species, direct damage, depending on the stage of plant development, can cause pod abortion or the formation of pods with smaller seeds and malformed (wrinkled and flat), consequently reducing the quality physiological effect of the seeds produced (lower germination and vigor), which can, including making areas unviable for seed production. Adding these damages direct to indirect caused by the presence of pathogens, there is also the rotting of seeds and pods, delayed maturation and increased occurrence of leaf retention, causing problems for mechanical harvesting and reducing productivity and grain quality.
Among the management strategies for the bed bug complex, Chemical control is the method usually used by farmers. In most Sometimes this control tactic is used without proper diagnosis of the population levels of these insects in crops, unnecessarily anticipating and increasing the number of insecticide applications and, consequently, the costs of production. Furthermore, the restricted number of efficient molecules for the control of bed bugs and the continued exposure of these populations to the same insecticides has promoted the selection of resistant individuals mainly for the brown stink bug, reducing the efficiency of this tool for managing adequate control of these insect populations.
An extremely useful tool for managing bed bugs lies in the use of resistant cultivars. Genetic resistance is the most simple and cheap for farmers, as it reduces production costs, brings environmental benefits and interacts positively with other methods of control. Unfortunately, the number of resistant cultivars registered in the Brazil is small and restricted to some specific regions (IAC-100 cultivars, IAC-17, IAC-24 and BRS 391). As it is a characteristic with more complex inheritance (Godoi & Pinheiro, 2009, Gen Mol Biology; Souza & Toledo, 1995, Braz J Genet.), the development of resistant and commercially competitive soybean cultivars have required great effort of research institutions. Considering an annual rate of productivity growth of 32,7 kg/ha in Brazil or 1,42% per year (Balbinot Júnior et al., 2017, R&D Bulletin / Embrapa Soja) it is easy to understand the challenge of inserting this resistance with polygenic inheritance into cultivars competitive. Fortunately, despite these technical difficulties, some institutions such as Embrapa have been able to make their contribution, already with a registered conventional cultivar in addition to lines derived from the various platforms worked at Embrapa (Conventional, RR and Intacta) with high productive potential and different levels of resistance to bedbugs (in the registration and validation).
A cultivar BRS 391 is a good example. This is early material (GM=6.4) with adaptation to the West, North and Northwest of Paraná, Middle Paranapanema and Southwest of São Paulo and South, Center-South and Southwest of Mato Grosso do Sul (RECs 201, 202 and 204), with average contents of 20,7% oil and 39,3% protein. AND resistant to the main soybean diseases (frog eye spot, stem canker, bacterial pustule and phytophthora root rot), root-knot nematodes (M. javanica e M. unexplained) and bedbugs. “Side by side” validation tests, with 2 hectare plots of each material, carried out in three producer areas in the 2014/15 harvest, presented yields between 5% and 44% higher than the cultivar BRS 232, reaching productivity of 5.910 kg/ha in Florínea, São Paulo (Table 1). In these locations, bedbug populations were monitored with the batting cloth and control chemical carried out when the population density of bed bugs reached the level of 4 stink bugs per meter, therefore, double the action level for commercial farming.
The first direct impact of the use of genetics is the reduction the number of insecticide applications. In Cândido Mota, two applications in BRS 391 against four applications in BRS 232 (Table 1 and Figure 1). In Florínea and Andirá, one and two applications were carried out, respectively, in two cultivars (Table 1). However, even with applications at the four bed bugs per meter, BRS 391 showed higher yield and lower percentage of chopped and unviable seeds in relation to BRS 232 (Table 1), indicating that the susceptible cultivar would need at least one additional application to avoid losses.
The second impact of this superior genetics is in improving physiological quality of the seeds produced. BRS 391 presented vigor and viability greater than or equal to the BRS 232 standard in Andirá and Florínea, respectively, providing a lower rate of chopped seeds and made unviable by bedbugs (Table 1). In the Cândido Mota area there was no difference between cultivars by tetrazolium analysis even with two fewer applications in BRS 391 (Table 1 and Figure 1).
Based on these validations carried out in commercial areas, it is clear that the cultivar BRS 391 tolerates twice the level of action recommended by management integrated pest control, requiring less use of insecticides.
Both in the conventional program and in the RR and Intact, there are already lineages with resistance/tolerance patterns to stink bugs superior to or equal to that of cultivar BRS 391. These strains exhibit agronomic cycle characteristics and productive potential to meet other soybean regions, such as macroregions 1 and 3. In competition trials in a network, the new strains have already had their productive potential proven and must go through a validation process in commercial areas to evaluate the impact on the management of bed bug populations. Among the conventional the BRI13-5301 and BR12-10309 lineages stand out, the latter also resistant to rust. For the RR program, the highlights are BRRI13-1533 and BRRI14‑1417 and for o Intacta, genotypes BRB15-232859 and BRB14-210725. That way, regardless of the platform desired by the farmer, it can be said that there will be no shortage of good competitive cultivar options, but with additional attributes to offer farmers an extra tool for managing populations of bedbugs in Brazil.
Carlos A. Arrabal Arias; Clara B. Hoffmann-Campo; Beatriz S. Corrêa-Ferreira; Ivani by O. Negrão Lopes, Embrapa Soya
Article published in issue 229 of Cultivar Grandes Culturas, June 2018.
Receive the latest agriculture news by email
Receive the latest agriculture news by email
Faced with the need to classify the level of sustainability of irrigated rice crops in different production systems, for example with rotation or not, the Rice Money Maker Championship arises
Adoption of biological control tactics and, in particular, the use of Baculovirus-based bioinsecticides for caterpillar management is an important complementary tool and in some cases even an alternative to other forms of pest control.
