Incidence, Characterization and Pathogenic Variability of Fusarium oxysporum in the Punjab Province of Pakistan

The present studies were conducted to determine the incidence of wilt caused by Fusarium oxysporum in the major chili-growing districts of Punjab, characterization of Fusarium isolates, and assessment of their pathogenic variability. The overall incidence of Fusarium wilt in the five major surveyed districts of the Punjab province was 9.2% in the year 2015-16 and 9.3% in the year 2016-17. The maximum disease incidence of 10.04% was recorded in district Multan in the year 2015-16 while it was the minimum (7.06%) in district Sahiwal. A similar trend was observed in the disease incidences during the year 2016-17. The disease incidences varied among different localities of the five districts. In total, 92 isolates were recovered from the chili crop in Punjab. All the recovered purified isolates were morphologically characterized using different parameters like colony color, growth habit, pigmentation, days to fill 9-cm-dish, concentric rings, size and shape of macroconidia and microconidia, phialide, septation in macroconidia, diameter, and formation of chlamydospores and interseptal distance. All the isolates were confirmed as Fusarium oxysporum. Based on the pathogenicity test, plants showing more than 75% wilting were rated as highly pathogenic, plants showing 50.1-75% wilting were pathogenic, plants showing 25.1-50% wilting were categorized as moderately pathogenic, and plants showing 0.1-25% wilting were graded as weakly pathogenic. The highly pathogenic and pathogenic isolates were subjected to molecular studies and all the isolates made a band of 550-600 on the gel. All the isolates showed 99-100% similarity with already reported Fusarium species. The phylogenetic tree showed a close relationship between all the isolates