Screening of Brassica juncea genotypes against downy mildew (Peronospora parasitica) using photoacoustic spectroscopy.

摘要

Thirteen B. juncea genotypes were studied for their response to P. parasitica. Plants were inoculated at the cotyledonary and true leaf stages with P. parasitica isolate (1.0x104 conidia/ml), incubated in a humid chamber (90-95% relative humidity and 15+or-2 degrees C) for 72 h, and examined for symptom development in greenhouse benches at 15-20 degrees C. After symptom development, approximately 1.0 cm2 of cotyledons and leaves (healthy and artificially infected) were cut and enclosed in the photoacoustic cell for recording the photoacoustic (PA) spectra using a 632.8-nm radiation of 10 mW linearly polarized He-Ne laser using chopping frequency from 5 to 400 Hz at a time constant of 30 seconds. The PA spectra of the cotyledons and leaves of inoculated plants of the various genotypes showed remarkable difference in their spectral pattern. The strength of the PA signal was greater for the diseased cotyledons and leaves than for the healthy cotyledons and leaves at all wavelengths examined. Genotypes showing higher PA signals were considered susceptible, whereas genotypes showing lower PA signals were considered resistant. Based on PA signals, the genotypes were categorized as resistant (EC-399296, EC-399299 and EC-399301), moderately resistant (EC-414322, EC-399294 and EC-399313), tolerant (EC-414324, EC-414310, EC-414305, Divya and PHR-1) and susceptible (Varuna and Kranti). The results were confirmed by epidemiological studies..