Characterization of grapevine root and trunk rot disease and the use of Trichoderma to promote plantlet rooting and growth

Abstract

Grapevine diseases are a concern for grape producers due to their economic impact. Among these, root and trunk rot, a new disease that has been observed during the cold storage of plantlets stands out. The disease reduces the quality of the plantlets and compromises their survival after definitive transplantation to the field. In this context, the development of new technologies applied to the production of grapevine planting material emerges as a promising approach to enhance the physiological quality of the grafted material. The use of biotechnological tools aimed at improving plantlet establishment can significantly contribute to mitigate losses in nurseries, favoring the initial vigor and rooting of the plantlets. The general objective of this research was to determine the etiology of root and trunk rot, as well as to test the potential of Trichoderma in the production of grapevine planting material. Initial observations indicated that fungi of the genus Fusarium were associated with the disease. Fingerprinting analyses by means of BOX-PCR of 86 Fusarium isolates from diseased plants revealed 45 genetic groups based on 53 polymorphic bands. Sequencing of tef1 gene fragments of 78 Fusarium isolates (30 from healthy plants and 49 from diseased plants) revealed 14 species belonging to the complexes F. oxysporum (FOSC), F. fujikuroi (FFSC), F. tricinctum (FTSC) and F. solani (FSSC). Pathogenicity tests in the field and greenhouse confirmed that 13 Fusarium species (F. casha, F. fredkrugeri, F. inflexum, F. vaughaniae, F. fujikuroi, F.annulatum, F. foetens, F. solani, F. landiae, F. triseptatum, F. guttiforme, F. annulatum and F.chongqingense) were able to cause root and trunk rot in grapevine plantlets. Comparative analyses of scanning electron microscopy showed that diseased plantlets had xylem vessels obstructed with tyloses and gum. Energy dispersive X-ray spectroscopy analyses showed differences in the mineral composition of roots of healthy and diseased plantlets. In healthy roots, Ca was distributed more uniformly and part of it was concentrated in the epidermis, while in diseased seedlings, it was in the xylem vessels. Silicon was not detected in healthy tissues, but was distributed uniformly in diseased tissues. In another part of the work, the Trichoderma isolate LFM004 was tested in a field experiment to promote rooting and growth of grapevine plantlets. It was observed that isolate LFM004 induced an increase in plantlet establishment of 98% and 55%, as well as an increase in root dry mass accumulation of 1.5× and 2.2×, compared to the water and hormone treatments, respectively. The isolate LFM004 was able to produce indoleacetic acid and solubilize phosphate, and these characteristics may be related to the activity of promoting rooting and growth of grapevine plantlets. The polyphasic characterization of isolate LFM004 through micromorphological and molecular analyses revealed that it was a new species, for which we proposed the name T. harenae sp. nov. The present study contributed to the description and characterization of a new grapevine disease, root and trunk rot, and also to the indication of a possible biotechnological solution to improve plantlets growth and establishment.