Abstract
Purple passion fruit, Passiflora edulis Sims f. edulis, is an important semi-perennial, fruit bearing vine originating in South America that produces a commercial tropical juice pulp for international and national consumption. Within the round purple passion fruit are a large number of membranous seed sacs each containing individual seeds. Little is known about the seed anatomy of the commercial passion fruit, differences between wild collected and commercial types, and its effect on seedling germination. Therefore, our main objective for this study was to analyze the seed anatomy variability of different germplasm as well as the effect on viability and germination of the seeds of this species. Germplasm was evaluated from three sources: (1) commercial cultivars grown in current production areas, (2) genebank accession from the national seed bank, and (3) landraces collected across different high and mid-elevation sites of the Andean region. A total of 12 morphometric descriptors related to seed anatomy were evaluated on the 56 genotypes, of which three were most informative: Angle to the vertex which is related to the shape of the seed, the thickness of the tegument and the horizontal length; separating the seed according to its source of origin. Germination was found to be positively correlated with the number (r = 0.789) and depth (r = 0.854) of seed pitting. Seeds of the commercial cultivars had more seed pits and higher germination compared to seeds of landraces or genebank accessions showing a possible effect of domestication on the crop. Interestingly, passion fruits often germinate during the rainy season as escaped or wild seedlings especially in the disturbed landscapes of coffee plantations, so some dormancy is needed but faster germination is needed for intensive cultivation. Harnessing passion fruit diversity would be useful as the semi-domesticated landraces have valuable adaptation characteristics to combine with rapid germination selected in the commercial cultivars. The variability of seed pitting with cultivars more pitted than landraces possibly resulting in faster germination may indicate that purple passion fruit is still undergoing a process of selection and domestication for this trait.
Highlights
Seed structural variability is related to germination capacity and can be a step in the process of domestication that distinguishes wild accessions from semi or fully domesticated crops (Koomneef et al, 2002)
Germplasm of purple passion fruit (P. edulis f. edulis Sims) was collected from three different sources: 8 commercial cultivars from farmers’ fields in the department of Cundinamarca and Boyacá, 14 genebank accessions were from the field grown in situ genebank collection kept by Agrosavia
Dry seed from the same source described above were evaluated for a total of 12 morphological traits: seven of these were morphometric descriptors suggested by Tangarife et al (2009), Santos et al (2014), Marostega et al (2017); while five were novel characteristics of seed shape and seed pitting that were new to this study
Summary
Seed structural variability is related to germination capacity and can be a step in the process of domestication that distinguishes wild accessions from semi or fully domesticated crops (Koomneef et al, 2002). Fruit crops propagated by seed may be subject to this type of selection given that they are often grown in hedgerows rather than in row crop agriculture. Purple Passion Fruit Seed Germination edulis Sims f. Edulis, is an important seed-propagated, semiperennial fruit bearing vine, which bears fleshy, and spherical “pepo type” berries with purple rinds that are filled with up to 200 small black seeds (Morton, 1987). The species originated in South America and exports from there and other tropical regions make it a major source of fruit pulp (Thokchom and Mandal, 2017). While passion fruit species can be propagated clonally (Salomão et al, 2002; Gelape et al, 2019), to date there are no seedless varieties and all are seed propagated or grafted onto seedlings.
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