Field response of some asparagus varieties to rust, Fusarium crown root rot, and violet root rot

Abstract

Research was carried out to evaluate the behaviour of some asparagus genotypes against three most important fungal diseases: 1) asparagus rust caused by Puccinia asparagi D.C.; 2) Fusarium crown and root rot caused by Fusarium oxysporum (Schlecht.) f.sp. asparagi (Cohen & Heald) and Fusarium proliferatum (Matstush.) Nirenberg; 3) violet root rot caused by Rhizoctonia violacea Tul. The object of this research was also to found an eventual correlation between the plant susceptibility to asparagus rust and the sensibility to Fusarium crown root rot and violet root rot attacks. Resistant genotypes to rust should be less susceptible to attacks from F. oxysporum f.sp. asparagi, F. proliferatum and R. violacea, a fungal complex causing the plant decline. Asparagus genotypes were compared in a randomized complete block experiment design, replicated four times, in order to search that ones showing the best behaviour to escape the diseases. Phytopathological observations were carried out on November when the control plots showed 100% infected plants. The pathogens were isolated and identified. The diseased plants were registered. According to symptom evaluation scales, all the plants were grouped into infection classes, calculating frequency and McKinney index. Wishing to learn something about the infection trend of F. oxysporum f.sp. asparagi or R. violacea in relation to P. asparagi attack, the relative curvilinear regressions were calculated. The Italian cultivars "Marte" and "Grande" showed significantly the best behaviour in terms of resistance to asparagus rust, exhibiting 37% and 42% of diseased plants. The McKinney index was 9.1% and 15.6%, respectively. The susceptible plots showed 100% of infected plants and different McKinney index: 46% for "Eros", about 60% for "H 519", "Atlas" and "Golia", over 70% for the remainder. "Marte" and "Grande" showed good tolerance to F. oxysporum f.sp. asparagi and to R. violacea exhibiting up to 100% of healthy plants. The regression between plants affected by asparagus rust and those diseased by Fusarium crown root rot showed a linear equation with a regression coefficient b = 1.186 and a correlation coefficient R2 = 0.98. The regression between infection caused by rust and that caused by violet root rot exhibited a regression coefficient b = 1.03 and a coefficient of correlation R2 = 0.9. "Marte" and "Grande" exhibited the best behaviour against the rust attacks. Plants without rust were tolerant to pathogens causing plant decline.