Mode of inheritance of fruit and stem color of the Italian heirloom ‘Rugosa Friulana’ Crookneck squash (Cucurbita pepo)

Abstract Crookneck squash, Cucurbita pepo subsp. ovifera , Crookneck Group, are a familiar produce item in the U.S.A. The Crookneck is an old group of cultivars, almost all of which have yellow young fruits that turn brilliant orange as they age, and dark-green-colored plant stems. ‘Rugosa Friulana’ (RFR) is an Italian heirloom that is unique among crookneck squash by retaining yellow fruit color throughout development and by having light-colored plant stems. The objective of this investigation was to determine the genetic basis of the persistent yellow fruit color and light stem color of RFR by crossing it with three near-isogenic lines of known fruit- and stem-color genotype. The results indicated that RFR is homozygous for gene Y , which confers yellow fruit color, and is unique among edible-fruited subsp. ovifera by being homozygous recessive at locus D , its d/d genotype conferring light-green stem color. The d/d genotype was confirmed by diagnostic PCR analysis of the causative CpAPRR2 ‑repeated locus. RFR also carries the uncommon top-dominant allele L-2 WS , which is partially epistatic to D in the stem and epistatic in the fruit and, by inhibiting green and orange coloration, results in the persistence of yellow fruit color through to fruit maturation. RFR segregates for the dominant allele conferring broad fruit stripes, l-1 BSt , or for a complementary gene necessary for expression of l-1 BSt . Two scenarios are discussed to account for the origin of the recessive d/d genotype of RFR. Hopefully, the ancestry of RFR can be determined in the future by whole-genome resequencing and comparative analysis.