Allelopathic effects of weed species extracts on some physiological parameters of wheat varieties

Effect of aqueous extracts of Ageratum conyzoides L., Chenopodium album L., Cynodon dactylon (L.) Pers., Melilotus alba L., Parthenium hysterophorus L., Phalaris minor L. and Solanum nigrum L. were examined on seedling dry weight, chlorophyll (a, b and total), carotenoid and proline content; net photosynthetic rate, net transpiration rate and stomatal resistance in PBW-154, PBW-343, PBW-373, PBW-443, PBW-502, RR-21, UP-262, UP-1109, UP-2382 and UP-2425 varieties of wheat (Triticum aestivum L.). The extracts of all weeds except C. dactylon and P. minor significantly decreased the seedling dry weight in all the varieties. The per cent reduction in chl-a was 100% of the varieties with A. conyzoides and S. nigrum; 90% with both C. dactylon and P. hysterophorus; 80% with M. alba; 70% with P. minor and 30% with C. album. But the percent reduction in chl-b was 80; 60; 50 and 20 per cent of the varieties with A. conyzoides, M. alba and S. nigrum; both P. hysterophorus and P. minor, C. dactylon and C. album, respectively. The proline content in different varieties was significantly increased with all weed extracts, except PBW-154 with C. dactylon; RR-21 with both C. album and C. dactylon and PBW-343, PBW-443 and UP-2382 with C. dactylon. The net photosynthetic rate (P) (μmol/m²/s); net transpiration rate (E) (mM/m²/s) and stomatal resistance (R) (m²s/mol) decreased in different varieties with all weed extracts as compared to control. Results revealed that PBW-154, PBW-373, PBW-443 and UP-1109 were resistant and others were susceptible. The inhibitory effects of weed extracts on different varieties followed the order: P. hysterophorus > M. alba > A. conyzoides > S. nigrum > C. album > P. minor and > C. dactylon.