Early detection of Meloidogyne exigua and bacteria diversities associated to egg masses of the pathogen in coffee

Abstract

Nematodes of the Meloidogyne genus cause severe damage to coffee crops. Among the species, Meloidogyne exigua is widely disseminated in Brazilian crops. Within integrated disease management planning, early detection of the nematode is one of the biggest challenges for producers. Furthermore, biological control is one of the pillars in integrated management and research involving interactions between the pathogen and microorganisms that inhabit the nematode egg mass are essential. Thus, the objective of this work was: to reveal the bacteria that inhabit the egg mass of M. exigua, in symptomatic and asymptomatic coffee plants regarding nematode attack, through sequencing of the 16S gene; and, evaluate the potential of remote sensing as a tool for the early diagnosis of M. exigua, through multispectral images collected with a remotely piloted aircraft (RPA) in two periods of the year (May – dry season, October – rainy season). Significant differences were found in the bacterial composition and diversity in the egg masses of symptomatic plants compared to asymptomatic ones. The families Pseudomonadaceae, Burkholderiaceae, Flavobacteriaceae, Rhizobiaceae, Micrococcaceae and Bacteroidaceae were more abundant in asymptomatic samples while Chitinopagaceae, Glycomycetaceae, Micropepsaceae, Beijerinckiaceae and Enterococcaceae were more abundant in symptomatic ones. The genera Pseudomonas, Sphingobacterium, Flavobacterium, Corynebacterium and Virgibacillus were found in greater abundance in asymptomatic samples, while only Tumebacillus and Bacillus were significant in symptomatic samples. The quality of the inoculum of the egg masses used in the trials was tested on tomato plants for infectivity and reproduction. Eggs per gram of roots were significantly reduced by inoculum from asymptomatic compared to symptomatic coffee plants, while root weight was significantly greater in tomatoes infected with inoculum from asymptomatic compared to symptomatic coffee plants. Based on the results obtained in the work with remote sensing, it was verified that the image parameters investigated demonstrated effectiveness in detecting infestation by M. exigua in coffee crops during the two different periods of the year. In both periods, a positive and statistically significant correlation was observed between the number of nematode galls and the red band. The GNDVI vegetation index showed a moderate and negative correlation with the number of nematode galls, and the NGRDI index showed a strong negative correlation with the number of nematode galls in both periods of the year evaluated. GNDVI was strongly negatively correlated with the number of nematode galls during the dry period. From the perspective of innovation, this research stands out for bringing new relevant information about bacteria that inhabit the M. exigua egg mass and the potential of remote sensing to detect the pathogen in the field.