Effect of year-to-year variation and genotype on trypsin inhibitor level in common bean (Phaseolus vulgaris L.) seeds

Changes in trypsin inhibitor (TI) level in common bean (Phaseolus vulgaris L.) seeds were investigated in relation to protein content, year-to-year variation and genotype. Twenty-one local populations from Basilicata region (southern Italy) were tested over 3 years (1995-97). The populations were cultivated in the same environment in which they were traditionally cultivated and are currently grown. A wide variation of TI content, expressed as untis of inhibitor per mg of dry matter (TIU mg-1 DM), was found within the populations of the collection (? ± 2?: 27.67 ± 2.72 in 1995, 25.31 ± 2.82 in 1996 and 23.39 ± 2.14 in 1997). It was found that 16 populations showed a decrease of TI level from 1995 to 1997, one population showed the opposite trend, in two populations the TI level remained unchanged, and in another two it reached its maximum in the intermediate year. A t-test showed that only the 1995-97 variation is highly significant (p<0.02). The increase of TI expression might possibly be related to the drought stress suffered by plants during the vegetative growth stage: rainfall received in 1995 during the growing season was lower (171 mm) than in 1996 (477 mm) and 1997 (388 mm); however, other aboitic or biotic factors cannot be excluded. It is suggested that the extent of TI variation contains a genetic component