Trifluralin-induced changes in hypocotyls of Phaseolus vulgaris in relation to lesion development caused by Rhizoctonia solani Kühn

Abstract

Treatment of sandy soil with trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at the rate of 1·12 kg ha−1 before planting seeds of Phaseolus vulgaris cv. “Sutter Pink” resulted in an increased size and number of hypocotyl lesions caused by Rhizoctonia solani Kuhn. The overall appearance of seedlings was also changed by trifluralin (T) treatment. Cortical cells developed isotropically instead of elongating as they did in untreated (N) seedlings; trichomes on T-hypocotyls never fully developed. Phosphate buffer extracts of lesions from both N- and T-hypocotyls showed maximum pectolytic activity at pH 4·0 on a pectin substrate. Cross-sectioned discs of N- and T-hypocotyls exposed to these lesion extracts exhibited increased maceration with time. Maceration of N-hypocotyls (measured with spectrophotometric readings of turbidity at 475 nm, light microscopy, and electron microscopy) proved greater than that of T-hypocotyls, even though T-hypocotyls are more susceptible to lesion development.