Zygospore production of RNAi mutants. A. Mating assays of the wild type strain NRRL3631 (+) with the (−) strains R7B (wild type, left) and rdrp-2Δ (right). Sexual interaction with formation of zygospores in the contacting zone (red arrow) can be only seen in the wild type cross. A histological section of the sexual interaction area observed under optical microscopy (10X) is shown. B. Relative zygospore production in genetic crosses between the indicated (−) strains and the wild-type NRRL3631 (+). Data are the averages and standard errors of the zygospores quantified in twelve histological sections (0.003 cm2) of the sexual interaction area for each cross after normalization against the zygospores produced in crosses between wild-type strains.