In the 1990s, innovative cross-breeding and classic genetic analysis of segregation ratios allowed advances in the understanding of host plant response to black leaf streak disease. Partial resistance owing to a recessive major gene (bs1 ) coupled with at least two additive minor genes (bsri ) appears to be durable because this genetic system slows disease development in the host plant. As a consequence, resistant hybrids show more healthy leaves, i.e. greater photosynthetic leaf area, than their ...