Embryogenic responses in anther derived calli of white and pink flesh guava (Psidium guajava L.) cultivars

Abstract

Androgenesis is reported in a few tree crops such as citrus and papaya; however, there is little information available about guava. Different modified Chu (N6) media and cold pretreatments of floral buds were tested to induce embryogenic calli in the anthers of two white flesh guava cultivars, ‘Round’ and ‘Pyriform’. Four modified Chu (N6) media formulations, i.e., M1 (400 mgL-1 casein hydrolysate, 200 mgL-1 glutamine, 0.2 mgL-1NAA, 1.0 mgL-1 KIN, 0.5 mgL-1 6-BAP, 0.5 mgL-1 zeatin and 5% coconut water), M2 (400 mgL-1 casein hydrolysate, 200 mgL-1 glutamine, 0.2 mgL-1NAA, 1.0 mgL-1 KIN, 0.5 mgL-1 6-BAP), M10 (0.5 mgL-1 2,4-D), and M11 (0.5 mgL-1 2,4-D and 50 mgL-1 PVP) enhanced anther swelling and callus formation. Genotypic variability was found in pollen viability, phenolic exudation, and anther tissue browning after cold pretreatment for 0-72 hrs. intervals. Anthers of ‘Round’ showed more pollen viability across cold pretreatment intervals with less phenolic exudations and tissue browning than ‘Pyriform’. On both M10 and M11 media, anthers with uni-nucleate microspores developed embryogenic calli; however, anthers of ‘Pyriform’ resulted in more calli induction (69.58%) on M10 media, whereas anthers of ‘Round’ developed more calli (66.60%) on M11 media. The proliferating calli in white flesh ‘Round’ and ‘Pyriform’ cultivars and pink flesh ‘Round’ cultivar formed more embryogenic masses upon transfer to growth hormone-free Chu (N6) media under light conditions; however, embryos showed delayed maturity with limited germination. More genotypes shall be explored to enhance embryo germination, and embryogenic media shall be further fine-tuned. This study provides the foundation for the generation of homozygous lines in guava using androgenesis