Two Varieties-X (Susceptible) and Y (Resistant)-Of Eggplant Were Used to Characterize

Multiple Choice

Two varieties-X (susceptible) and Y (resistant) -of eggplant were used to characterize the genetics of resistance to a necrotizing plant pathogen. Eight thousand plants from each variety were inoculated, and the average number of necrotic lesions produced per leaf was recorded. Variety X averaged 52 lesions per leaf, whereas variety Y averaged six lesions per leaf. The F₁ progeny from a cross between variety X and variety Y plants averaged 21 lesions per leaf, with a standard deviation of 3.7. Of the F₂ progeny, 8000 were again tested by inoculation, and a total of four plants produced were phenotypically similar to the original parental plants-two plants for each extreme (i.e., parental) phenotype. Overall, the F₂ plants averaged 18 lesions per leaf with a standard deviation of 7.5.
-How many gene pairs control resistance to this pathogen?

A) two
B) four
C) five
D) six
E) nine