ABSTRACT

Tomato (Solanum lycopersicum L.) is an important vegetable crop, affected by early blight caused by Alternaria spp. causing yield losses up to 80 % in tomato
A roving survey conducted in Dharwad, Belagavi, Bagalkot, Gadag and Vijayapura districts of northern Karnataka indicated that higher severity of early blight was recorded in Dharwad district (47.44 and 34.35 %) during kharif 2021and kharif 2022, respectively. Whereas least disease severity was noticed in Bagalkote (32.71%) during kharif 2021, while in kharif 2022, Gadag district recorded the least severity of (17.52%). In Dharwad district, the survey was also conducted during rabi 2021and 2022, as well as in summer 2022 and 2023 where maximum per cent disease index was observed during rabi 2021 and 2022 (17.62 and 16.55, respectively) compared to summer 2022 and 2023 (7.33 and 13.06 %, respectively).
Highest per cent reduction in disease severity was recorded in DMT 5 (66.26 %) genotype while lowest was recorded in DMT 1 (62.99 %). Highest per cent reduction in number of fruits were recorded in the genotype DMT 2 (57.14 %) and least was found in DMT 5 (41.61 %). highest reduction in fruit yield per plant was recorded in DMT 1 (72.83 %) and lowest was recorded in DMT 5 (59.84 %). Highest per cent loss in fruit yield was recorded in DMT 1 (72.82 %) and lowest was recorded in DMT 5 (59.83 %).
Sixteen isolates of Alternaria showed cultural variations in colony colour (whitish grey to grey), margin type (irregular to regular), mycelial growth (flat to raised) texture (smooth to coarse) with variation in growth rate. Morphological variations in the conidial size, beak size and number of septa in conidia and sporulation pattern were also observed within the isolates with muriform shaped conidia. Molecular variability using pathogen specific primers (AS1 and AS2) identified 15 isolates as Alternaria alternate and one isolate as Alternaria solani. Based on phylogenetic analysis, isolate DhaAl-1 was closely related with the TimAl-6 isolate. On the basis of virulence, 16 isolates were classified into three groups. Group I (highly virulent) consisted ShaAl-3, AttAl-4, BanAl-9, NarAl-11 and PanAl-15. Group II (moderately virulent) included DhaAl-1, DhuAl-2, NicAl-5, AnaAl-10 and WadAl-16. Group III (less virulent) consisted of TimAl-6, KirAl-7, IncAl-8, NarAl-12, KarAl-13 and VelAl-14.
Based on in vitro studies, mancozeb 75% WP @ 0.25%, (captan 70% + hexaconazole 5%) 75% WP @ 0.2%, elixir @ 1.0% , Trichoderma harzianum @ 1.0% and panchagavya @ 10% were included in spray schedule. Four sprays of (captan 70% + hexaconazole 5%) 75% WP @ 0.2% recorded least per cent disease index of 33.14, higher fruit yield of 45.38 t ha-1 and maximum cost: benefit ratio of 1: 5.02 followed by four sprays of mancozeb @ 0.25% (42.55 PDI) ( 36.42 t ha-1) (1: 4.07 BC: ratio). Out of 200 tomato genotypes screened none of them showed immune or highly resistant reaction, one showed moderately resistant reaction, 90 showed moderately susceptible reaction, 63 showed susceptible reaction and 46 were found highly susceptible to early blight.