Fusarium spp. and inoculum load estimation associated to commercial Agave tequilana offsets at different regional epidemic inductivity levels

Abstract

The research objective was to identify the Fusarium specie(s) associated with commercial offsets of Agave tequilana and to develop a methodology to quantify the inoculum load in offsets from Jalisco mother plantations with differential epidemic inductivity to wilt and dry bud rot syndrome (SMAP). The purpose was to provide criteria for the certification of mother plantations. The samples were collect between March and May in 2018 and 2019, from 21 commercial plantations of 14 municipalities of Los Altos, South, and Valley of Jalisco. The number of diseased plants (PE) and SMAP severity (S) were estimated in 63 and 200 plants/plantation using App-SIVEA for 2018 and 2019 respectively. The CIFUSAG method was developed and applied in 7055 offsets and 46656 fungal colonies obtained from 2364 basal ‘piña’ wash isolates, internal tissue sections, and offset total maceration. Colony Forming Units (CFU) of Fusarium spp. (Fsp) and total fungi (HT), purification, monosporic, morphological and cultural characterization was made with Komada, water-agar, Sabouraud, SNA, and Sabouraud media, respectively, selecting 557 contrasting isolates. The highest epidemic inductivity in Los Altos was associated to moderate Fusarium Index [(FI) = (?Fsp) / (?HT)] (0.30 and 0.40) and Fsp (20 and 72 CFU) compared to South, which had higher values (0.69, 0.50; 23, 84 CFU, respectively) (Tukey p=0.05). The offset base-size had no influence on FI and Fsp (p=0.183). FI and Fsp of basal ‘piña’ washing were not correlated with S in mother plants (r2 = 0.036 and 0.13), while PE only was correlated with Fsp (r2 = 0.94). The inoculum load obtained by washing was higher than internal tissue with a total of 17,828 CFU (93%) and FI=0.42. Molecular analysis with the EF-1a gene showed an association of 23 isolates with four phylogenetic complexes: Fusarium oxysporum, F. fujikuroi, F. solani and F. incarnatum-equiseti with identity greater than 98%. Offsets of Agave tequilana constitutes a dispersal factor of at least four species of Fusarium spp. in the range of 3.3±3 y 6.83±4.2 CFU/offset.