Susceptibilidad al mildiu de variedades de vid PIWI a campo bajo diferentes manejos fitosanitarios y en laboratorio en condiciones controladas

Downy mildiu (Plasmopara viticola) is one of the most common fungal diseases that affect vine production, particularly in areas that get precipitation throughout the growing season. The management of this disease requires the use of several chemicals, resulting in higher expenses as well as an adverse environmental impact. Grape varietals known as PIWI have arisen in recent decades that are resistant to fungi-caused illnesses. These stand out due to their high Vitis vinifera genome content, preservation of the bigger resistance genes from American or Asian vines and oenological quality. The aim of this study was to evaluate the sensitivity of 8 PIWI cultivars to the downy mildew under various management and production situations in Uruguay. Five white grape varieties (Fleurtai, Soreli, Sauvignon Kretos, Sauvignon Nepis, and Sauvignon Rytos) and three black grape types (Cabernet Volos, Julius, and UD 72-096) were tested. All of the evaluated grape varieties came from the Vivai Cooperativi Rauscedo, Udine, Italy. Only one of the varieties in this group, which mostly possesses monogenic resistance to P. viticola, carries both resistance loci Rpv 3 and Rpv 12. (Soreli). There were three managements: two under field conditions, the first with integrated management (C4) and the other with reduced use of fungicides to control downy mildew (C3); the third under laboratory conditions on detached leaf. The evaluations were completed during 2021–2022, and the investigations were carried out at the Experimental Station INIA Las Brujas, Canelones, Uruguay. Four totally random blocks (DBCA) with six-story plots served as the experimental unit in the field experiment. The incidence and severity of downy mildiu of a medium vigor shoot were evaluated on four central plants, on the 5, 10, 15, and 20 leaves, counting from the shoot top. For severity, a six-category scale (0 to 5) was employed, with 0 representing no symptoms and 5 representing more than 75% of the leaf with symptoms. The PIWI cultivars Cabernet Volos, Fleurtai, Julius, Sauvignon Kretos, and Soreli all bore the locus Rpv 12 and showed a lesser severity when fungicides were used sparingly to control this disease. In contrast, when the integrates management were applied, severity was kept to a minimum in all the varieties. Under laboratory conditions, the experimental design was a totally randomized design (DCA) using 40 Petri dishes as experimental units, with severity measured as a percentage of infected droplets. The severity in this study never exceeded 50% in any of the varieties, confirming the resistance conferred by the Rpv gene. As part of integrated management, the introduction of resistant PIWI varieties with less usage of phytosanitary treatments brings enhanced environmental sustainability and lower production costs while retaining oenological quality.