Field reactions of interspecific hybrids of tomato (Solanum lycopersicon Mill.) lines to leaf spot disease
Leaf spot is a major disease of tomato causing reduction in fruit yield under humid environments. It's control using some of the major systemic fungicides available is environmentally unfriendly and costly. Heterosis known to increase productivity in crops was used to assess improvement in tomato yield and resistance to leaf spot disease. Crosses were made on four selected parent plants in a diallel fashion in 2011. Seedlings of the parent plants and their resulting hybrids were established in a field in a randomized complete block design with three replications in 2012. The leaves were assayed at the vegetative and reproductive stages for leaf spot infection and some phytochemicals content. Data obtained were subjected to analysis of variance, correlation and path analysis to partition the effects to the causes. Better parent heterosis (BPH) was obtained at both stages of growth. The disease incidence and severity amongst the hybrids were significantly (p= 0.05) reduced in all crosses with wild as the pistillate parent relative to others. The hybrid, wild x petomech (W x P) had significantly higher phenol content of 4.29 mg/100g, highest negative BPH of -30.40% and lower in disease severity. Flavonoid showed a positive and significant correlation with phenol (r= 0.51, n= 39, p= 0.01). There was a high direct (0.98) and indirect (1.0) effects of flavonoid to fruit yield through disease severity at fruit ripening. The hybrids, W x P and wild x insulata could be selected as they had less leaf spot disease severity and high fruit yield.
Keywords: disease incidence, disease severity, heterosis, phytochemicals and wild tomato