Nematoide das galhas (Meloidogyne javanica) na cultura da batata: período de cultivo e dinâmica populacional, qualidade dos tubérculos e alterações histopatológicas em diferentes genótipos.

Abstract

In order to prospect management measures of root -knot nematodes (Meloidogyne javanica), to assess tuber quality and possible histopathological changes on tissues infected by root-knot nematodes this study was done. The thesis is divided in three chapters. The objective of the first study was to evaluate the reaction of different potato genotypes to M. javanica (Est J3) and its damage on potato tubers at greenhouse conditions and to study the population dynamics of the root-knot nematode in a naturally infested area in three cropping seasons. In the second study, the objective was to evaluate the effect of different levels of M. javanica inoculum on its reproduction, damage and chemical and biochemical changes in the potato tubers of cultivars Asterix, BRSIPR Bel and BRS Clara infected by the nematode. In the third study, the objective was to evaluate visual, sensorial and histopathological changes in infected potato tubers with the root-knot nematode, and the damaged caused in different periods after harvesting. In the first study, potato plants of cv. BRS Clara, established in field plots, in naturally infested soil with M. javanica, an experiment was carried out to evaluate the nematode population fluctuation in different planting periods of the year. Concomitantly, using a very aggressive M. javanica population, in greenhouse, the reaction of ten potato genotypes and the damage caused in the tubers were evaluated. Finally, an experiment at greenhouse conditions was carry out to study the influence of different levels of M. javanica inoculum on the quality of potato tubers of Asterix, BRSIPR Bel and BRS Clara cultivars, chlorophyll index, rate of nematode reproduction in the roots and tubers, besides other variables. From the tubers produced by the three potato cultivars, the content of phenolics compounds and antioxidant activity, starch, glucose, sucrose, and dry matter content were evaluated. The influence of post-harvest storage time of infected tubers on tuber internal visual quality was also evaluated, as well as the histopathology and the relations between de inoculum level and the potato cultivar on the sensorial and visual traits in potato chips and cooked. In the field experiment, the highest population levels of M. javanica were observed in the first growing period (from 20.08.2013 to 23.11.2013), when the average daily temperature was higher (24.2°C) compared to the other periods, which may have favored the development and reproduction of nematodes in the roots of potato plants. All potato genotypes behaved as susceptible to M. javanica [reproduction factor (RF)> 1.00], however it was verified different levels of susceptibility among the tested materials. Evaluating the influence of different levels of M. javanica inoculum on the different potato cultivars, there was a significant interaction between the treatmen ts for most analyzed variables. In general, independently of potato cultivar, higher levels of nematode inoculum resulted in higher number of galls in the roots, higher number of galls per area unity, and tendency to of reduction factor values with increase of inoculum level. Additionally, it was verified that plants inoculated with 1250 or more nematode eggs + J2, in general, presented reduction on fresh mass of aerial part (FMAP) and fresh root mass (FRM). Higher content of phenolic compounds was found in tubers of Asterix and BRS Clara cultivars comparing to control and to the plants inoculated with the lowest level of nematode inoculum (625 eggs + J2 of M. javanica). Higher antioxidant activity was observed in potato tubers of Asterix and BRS Clara, with the highest and lowest level of inoculum tested, respectively; while for BRSIPR Bel there was no significant difference between the levels of inoculum. In relation to starch content, there were significant differences among inoculum levels only for BRS Clara, while for glucose and sucrose content, there was an increase in these carbohydrates in the tubers with higher M. javanica inoculum levels for BRSIPR Bel and BRS Clara, and for all treatments with Asterix where there was inoculation of eggs+J2 of M. javanica. This result indicates increase in the content of reducing and non-reducing sugars as a result of the parasitism by nematode. Furthermore, there was a progressive increase of theses darkened regions and the presence of rot in the tubers with increasing storage period. Evaluating the processed tubers as chips and cooked, it was verified that all sensorial and visual traits were affected by the root-knot nematode. Histopathological analysis of cross sections of galls from the roots with M. javanica revealed the formation of giant cells in the vascular cylinder, six in number, multinucleated, and with prominent nucleoli, independently of the potato cultivar. Histological changes observed in the potato tubers were similar to those produced by nematodes on the roots; however, there has been a greater amount of mucilage in this region, besides cellular disorganization, formation of giant cells, cell wall degradation, and the presence of more than one nucleolus per nucleous.