Somatic Embryogenesis and Regeneration from Cotyledon Explants of Six Squash Cultivars

Abstract

Six summer squash (Cucurbita pepo L.) cultivars were regenerated via somatic embryogenesis using cotyledons excised from germinated or nongerminated seeds. Genotypes included were zucchini, commercial F1 hybrids, `President', `Seneca Zucchini', `Jade'; the noncommercial inbred line `Caserta Inbred 557311'; and two yellow squash hybrids `Dixie' and `Seneca Butterbar'. Somatic embryogenesis was initiated in induction medium containing 22.62 μm 2, 4-D, and embryos were germinated in maturation medium containing 0.27 μm NAA and 0.23 μm kinetin. Plants were elongated and rooted on basal medium without hormones. All media contained carbenicillin at 500 mg·liter–1. Sixty-one percent of the `Seneca Butterbar' cotyledons produced somatic embryos when kept on induction medium for 10 weeks. Overall, 7% of the initial explants produced plantlets, and regeneration efficiency was calculated as 0.3 plantlets per initial explant. The relative production of plants from cotyledons that were kept on induction medium for different time periods were determined for `Caserta Inbred 557311' and `Seneca Zucchini'. All cotyledons produced somatic embryos after 11 to 17 weeks on induction medium. However, plantlet production was optimal with explants kept on induction medium for 13 weeks for `Seneca Zucchini' and for 15 weeks for `Caserta Inbred 557311', producing an average of 4.5 and 9.3 plants per explant, respectively, from 90% to 70% of the explants. We recovered plants from all six cultivars; thus, our regeneration protocol may be applicable to other genotypes. The high percentage of regenerants obtained indicates that the regeneration method is efficient enough to be adapted successfully to squash transformation experiments. Chemical names used: α-carboxybenzylpenicillin (carbenicillin); 2,4-dichlorophenoxyacetic acid (2,4-D); 6-furfurylaminopurine (kinetin); α-napthaleneacetic acid (NAA).