Abstract
Cycas micronesica is a foundation species in several Micronesian islands and its seeds have been a historical source of starch for the island residents. The species has become endangered by invasive specialist insect herbivores and conservationists struggle with the inability to estimate the age of observed seeds. To inform this agenda, we evaluated numerous Cycas micronesica seed traits to determine if any exhibited a relationship with age and a substantial change in absolute value. Of the 30 direct and derived seed traits that we evaluated, most of them were non-linear and exhibited minimal change after about 12 months in age. The only traits that emerged as unambiguous estimators of age were the quotients derived as gametophyte fresh weight/total seed fresh weight and sarcotesta dry weight/sclerotesta dry weight. These two simple metrics can be used to accurately estimate seed age for this arborescent cycad species.
Highlights
Fruit maturity standards are critical components of various horticulture production systems in order to maximize fresh quality, post-harvest shelf-life or processing success [1,2]
The tissues of the cycad seed are spatially separable into the sarcotesta, which is the soft external tissues of the integument, the sclerotesta, which is the hard internal tissues of the integument and the gametophyte which develops inside the sclerotesta [6]
The C. micronesica seed is separated into integuments comprised of diploid maternal tissues, gametophytes comprised of haploid tissues and diploid embryos (Figures 1 and 2)
Summary
Fruit maturity standards are critical components of various horticulture production systems in order to maximize fresh quality, post-harvest shelf-life or processing success [1,2]. The assessment tools developed for determining fruit ripeness rely on contrasting approaches. Maturity standards are important for understanding gymnosperm seed development as for angiosperm fruit development. The tissues of the cycad seed are spatially separable into the sarcotesta, which is the soft external tissues of the integument, the sclerotesta, which is the hard internal tissues of the integument and the gametophyte which develops inside the sclerotesta [6]. The embryo develops inside the gametophyte structure and often matures only after abscission of the seed. Several Cycas L. species belong to a complex which produces seeds that float to enable oceanic dispersal [6]. The tissues that enable flotation in the seeds of these species are spatially distinct and develop between the sclerotesta and gametophyte
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