Microbialization control

Blast is an extremely aggressive disease in rice cultivation, responsible for losses of up to 100% in situations of severe incidence. The search for strategies such as the use of microbiolized bacteria in seeds appears as an alternative to increase integrated management options, improve the initial development of plants and reduce the severity of the pathogen on leaves.

At all stages of its development, rice is subject to biotic and abiotic stresses. Among the biotic diseases, diseases that reduce the productivity and quality of grains stand out, blast being the main one. Caused by fungus Magnaporthe oryzae (Pyricularia oryzae – anamorphic), blast is the most significant disease in Brazil and the world, occurring throughout the national territory. In the Central-West region, where the highland cultivation system predominates and environmental conditions favorable to the development of the disease, the losses are greater, with 100% losses possible, depending on the cultivar and cultivation conditions. Genetic resistance is considered the most economical and ecologically correct strategy to minimize losses caused by the disease in rice plants. However, blast control is carried out using agrochemicals, which are not always specific to the pathogen. The effectiveness of plant protection is linked to the type of fungicide used, the application interval, the number of applications, the application time, the mixtures used and the quality and technology of the application. The fungicide used must be toxic only to the target pathogen and have a low environmental impact.

Studies carried out at Embrapa Arroz e Feijão, in 2011, to test the effect of four fungicides on non-target fungi of the rice phylloplane, found that, of the fungicides tested, two reduced the severity of panicle blast and only one showed a certain degree of selectivity to the pathogen, not affecting the development of non-target fungi on the leaf. Thus, there is a need for integration of control methods, integrated management. This management aims to reduce the pathogen population to tolerable levels, without causing economic damage to the crop, through the adoption of a set of preventive measures, in a non-isolated manner. The main component of management is the genetic resistance of the cultivar, followed by chemical control, cultural practices and, more recently, biological control. Interest in biological control has increased recently with the aim of finding options other than chemical control. With the objective of evaluating blast symptoms and initial development in rice plants, seeds of the Primavera cultivar were microbiolized with bacteria previously isolated from the rhizosphere of rice (R235 and R46) and eucalyptus (RE1 and RE8). Seed microbiolization was carried out by keeping the seeds immersed in a bacterial suspension for 24 hours under constant agitation. Subsequently, the seeds were dried at room temperature for 24 hours and then sown in pots (Figure 1) containing 8kg of soil, sifted and fertilized at a rate of 350kg/ha using the formula N-P-K (05-30-15). For control purposes, non-microbiolized seeds were also sown, with part of the treatments inoculated with water. For the development of blast, after opening the third leaf, inoculation was carried out with a suspension of conidia of M. oryzae 3 x 10⁵ conidia.ml^-1. The experiment totaled 10 treatments, namely: T1) non-microbiolized seeds inoculated with M. oryzae; T2) non-microbiolized seeds inoculated with water; T3) microbiolized seeds with R46 inoculated with water; T4) microbiolized seeds with RE8 inoculated with water; T5) microbiolized seeds with RE1 inoculated with water; T6) microbiolized seeds with R235 inoculated with water; T7) microbiolized seeds with R46 inoculated with M. oryzae; T8) microbiolized seeds with RE8 inoculated with M. oryzae; T9) microbiolized seeds with RE1 inoculated with M. oryzae; and T10 seeds microbiolized with R235 inoculated with M. oryzae. Nine days after inoculation, leaf blast was assessed and three plants were collected per pot from each treatment. They were measured from the neck to the apex of the largest leaf to evaluate plant development and the data was subjected to analysis of variance.

The analyzes carried out showed the occurrence of a negative interaction between plant size and leaf blast severity (BF) when the seeds were microbiolized with rhizobacteria (Figure 2A), that is, the greater the severity of leaf blast, the smaller the size of the plants. . Another result evidenced by the analysis of variance was a significant difference between the treatments, indicating that the size of the plants was influenced by the presence of the rhizobacteria R46 (from the rice rhizosphere) and RE8 (from the eucalyptus rhizosphere), a variation observed by the Tukey test at 5 % probability (Figure 2B). The analysis of variance for leaf blast severity showed statistical differences for all treatments in relation to the inoculated control (T1), with CV = 20,81% (Figure 3). Isolate R46 reduced leaf blast severity by 33%, followed by isolate RE8 (20%), and also increased plant size by 42% and 31%, respectively, when compared to the control. Studies to identify these bacteria are being carried out by Embrapa Arroz e Feijão, as well as the use of these bacterial isolates in the control of other rice pathogens and also in the development of plants and control of diseases in other crops. These results indicate that the use of bacteria via seed microbiolization is a good alternative for the initial development of rice plants in addition to significantly reducing the severity of leaf blast. This practice can reduce the use of agrochemicals in the crop, once it is introduced into integrated disease management.

Figure 1 - Rice plants before inoculation (A) and after inoculation (B)

Figure 2 - Severity of leaf blast in treatments 2 - non-microbiolized seeds inoculated with water (A), 7 - microbiolized seeds with R46 inoculated with M. oryzae (B); 8 - microbiolized seeds with RE8 inoculated with M. oryzae (C), in relation to treatments and 1 - non-microbiolized seeds inoculated with M. oryzae (D)

Rice

The rice (Oryza sativa) is a staple food for about half of the world's population, being the product of greatest economic importance in many developing countries. Estimates indicate that by 2050, production will have to double to meet the population's demand and Latin America and Africa stand out as the only regions with potential for rice production with the capacity to meet the growth in consumption by the population. It stands out for its adaptability to the most diverse ecosystems, the breadth of its occupied area, as well as its productivity, both in Brazil and around the world.

This article was published in issue 182 of Cultivar Grandes Culturas magazine. Click here to read the edition.