Inheritance of chilling injury: A maternally inherited trait in cucumber

Chilling temperatures (≤12°C) can cause substantial economic damage to cucumber (Cucumis sativus L.) plants. Previous studies suggest chilling tolerance trait is controlled by nuclear gene(s). To investigate inheritance of chilling injury in cucumber, cucumber lines [susceptible GY14 (P₁), tolerant 'Chipper' (P₂), and tolerant 'Little John' (P₃)], and their exact reciprocal F₁ and F₂ cross-progeny were evaluated to determine the inheritance of chilling injury at the first true-leaf stage when challenged at 4°C for 5.5 hours. The mean chilling ratings [1(trace) to 9(dead)] of progeny comparisons were F₁(P₁ × P₂) = 6.2 vs. F₁(P₂ × P₁) = 1.6; F₂(P₁ × P₂) = 6.4 vs. F₂(P₂ × P₁) = 2.7; F₁(P₁ × P₃) = 5.4 vs. F₁(P₃ × P₁) = 1.7; and F₂(P₁ × P₃) = 5.8 vs. F₂(P₃ × P₁) = 2.2. These data suggest that chilling tolerance was maternally inherited as is the chloroplast genome in cucumber. Parents, reciprocal F₁, and F₂ progeny were evaluated for variation using random amplified polymorphism DNA (RAPD). Although no maternally inherited RAPD markers were detected, polymorphic and paternally inherited RAPD bands AD2₁₂₄₉, AV8₉₁₆, and AV8₉₆₉ amplified by AD2 and AV8 primers were cloned and sequenced. A BLAST search of these sequences suggested that their origin is likely cucumber mitochondrial DNA. These results indicate that the mitochondria genome is not associated with the chilling tolerant trait because this genome is paternally inherited in progeny derived from this reciprocal mating. Therefore, the results of maternally inherited chilling tolerant trait and paternally transmitted mitochondria genome support that the chilling tolerant trait as identified is likely associated with the chloroplast genome which is maternally transmitted in cucumber.