Biomass Partitioning and Seed Yield in Hybrid Snackseed Pumpkins

Abstract

A field study was conducted to compare seed yield and fruit biomass partitioning among 11 F1 hybrid snackseed (hull-less seeded) pumpkins. Experimental plots were seeded on 3 June 1999, using a randomized complete-block design with four replications and 20 plants per plot. Rows were spaced 1.8 m apart; within-row spacing was 0.3 m. The plots were divided in half with 10 plants for fruit and seed yield determinations and 10 plants for fruit biomass partitioning studies. Seed yields among hybrids ranged from 818 kg·ha-1 for NH1003 to 1575 kg·ha-1 for NH1041. The three highest-yielding hybrids (NH1030, NH1040, and NH1041) were derived from sister lines crossed to a common parent and were characterized by small fruit size (0.8 to 1.4 kg) and high seed biomass per kilogram of fruit fresh weight. The next highest-yielding group of hybrids (NH1024, NH1043, NH1044, and NH1045) also had small fruit, and two pairs of hybrids, NH1024/NH1043 and NH1044/NH1045, each shared a common parent. The four lowest-yielding hybrids (NH1003, NH1025, NH1027, and NH1029) were characterized by larger fruit (2 to 3 kg) and low seed yield per kilogram fruit fresh weight, but had larger seeds (average between 175 to 183 mg) than the other hybrids (130 to 165 mg). Peak percent dry matter of mesocarp tissue at 35 days postanthesis (PA) was lowest in large-fruited hybrids and highest in the highest-yielding hybrids. In most hybrids, percent dry matter decreased between 35 days PA and fruit maturity (65 days PA), indicating a shortage of photosythates needed for maintaining mesocarp biomass and maximizing seed fill. The highest-yielding varieties partitioned a greater portion of fruit biomass into seeds rather than flesh. Seed yield per plot was highly correlated with seed yield per kilogram of fruit fresh weight.