Population Dynamics of Aspergillus Section Nigri Species on Vineyard Samples of Grapes and Raisins

Abstract

Several species of Aspergillus section Nigri, including potential mycotoxin producers, are common residents of grape vineyards, but the relative population size of individual species throughout the growing season is difficult to determine using traditional isolation and identification methods. Using a quantitative droplet digital PCR (ddPCR) method in combination with dilution plating, total Aspergillus section Nigri populations and relative proportions of A. niger, A. welwitschiae, A. carbonarius, and A. tubingensis were measured from vineyard samples without the need for identifying individual fungal isolates. Grapes were sampled from two raisin vineyards (vineyards A and B) at berry set, veraison, harvest, and raisin stages in two consecutive years. Plate counts showed that the total population of Aspergillus section Nigri present on the fruit increased from berry set to raisin and became a larger component of the total recovered fungal population in both vineyards in both years. Results from ddPCR analysis showed that the relative proportion of A. carbonarius among the four species assayed increased later in the season (harvest and raisin) in comparison to earlier in the season (berry set and veraison). Total fungal and Aspergillus section Nigri plate counts were not significantly different between vineyards in either year. However, vineyard A generally showed higher proportions of A. carbonarius in harvest and raisin samples than vineyard B. This coincided with higher incidence and levels of ochratoxin A in vineyard A harvest and raisin fruit than in vineyard B fruit. This work demonstrates that this ddPCR method is a useful tool for culture-independent monitoring of populations of mycotoxigenic Aspergillus species during grape and raisin production.

Improved Detection and Monitoring of Fungicide Resistance in Blumeria graminis f. sp. hordei With High-Throughput Genotype Quantification by Digital PCR

“…Applications of dPCR for agriculture are emerging, and include screening for genetically modified organisms in seed samples ( Fu et al, 2015 ), studies on populations dynamics of four species of Aspergillus infection on grapes ( Palumbo et al, 2016 ), detection of low levels of Phytophthora nicotianae in environmental samples ( Blaya et al, 2016 ) and studies of virus transmission and infection on grape vines ( Bahder et al, 2016 ). However, to our knowledge, no studies to date have used dPCR to detect fungicide resistance in field samples of crop plants.…”

Rapid and accurate identification of black aspergilli from grapes using high‐resolution melting (HRM) analysis

“…Previous studies have shown that among the Aspergillus section Nigri species described, 11 have been described and isolated from grapes, with A. carbonarius , A. tubingensis and A. niger being those with the highest occurrence and representation, and A. carbonarius the predominant species regarding OTA production and contamination of grapes . The necessity for determination of the most common black aspergilli in grapes has led to the development of numerous endpoint and real‐time PCR methods capable of detecting the species of interest.…”

“…Previous studies have shown that among the Aspergillus section Nigri species described, 11 have been described and isolated from grapes, with A. carbonarius, A. tubingensis and A. niger being those with the highest occurrence and representation, and A. carbonarius the predominant species regarding OTA production and contamination of grapes. 2,5,35 The necessity for determination of the most common black aspergilli in grapes has led to the development of numerous endpoint and real-time PCR methods capable of detecting the species of interest. These methods have proved accurate and replicable; however, although allowing the detection of certain Aspergillus species set as specific targets in each PCR assay, in the case of end-point PCR they are laborious since they require more than one step for the analysis.…”

Genetic Diversity, Ochratoxin A and Fumonisin Profiles of Strains of Aspergillus Section Nigri Isolated from Dried Vine Fruits

“…Fourteen out of the twenty-seven currently recognised black aspergilli have been documented as colonisers of dried vine fruits up to date [ 5 , 32 , 33 , 34 , 35 ]. Nevertheless, only a few studies reported more than five species from one type of substrate [ 31 , 32 , 33 , 34 , 35 , 36 ]. The most dominant and, simultaneously, most genetically diverse species in our study (fourteen genotypes) was A. tubingensis .…”