Abstract
Pomegranate cultivation has expanded significantly in the last two decades. However, there is limited information on its fertilization requirements and the effect of macronutrient availability on its reproductive development. Two commercial pomegranate cultivars—“Wonderful” and “Emek”—were grown in 500-L containers for 3 years, using a fertigation system. Development and reproduction indices were measured to explore the trees’ responses to elevated levels of nitrogen (N), phosphorus (P) and potassium (K) in the irrigation solution. Andromonoecy rate was affected by nutrient levels only in the first year of the experiment, with higher levels of N and P leading to a greater proportion of hermaphrodites out of total flowers. P level had a positive effect on the total number of hermaphrodites per tree in both varieties. Differences recorded between hermaphroditic and staminate flowers included nutrient concentrations and dry weight. Fruit set and aril number were positively affected by N concentration in the irrigation solution. We conclude that only a severe deficiency of N and P affects the andromonoecy trait, and that at the levels examined in this study, K hardly influences pomegranate reproduction.
Highlights
About 2% of known plant species are andromonoecious—a floral dimorphic sexual system in which an individual plant bears both hermaphroditic and staminate flowers [1].Several evolutionary explanations for andromonoecy have been suggested
Another hypothesis is that male flowers are more attractive to pollinating insects, and andromonoecy increases the chances of pollinators reaching these flowers and carrying the pollen [4]
The concentrations of sulfur (S), iron (Fe), manganese (Mn), and zinc (Zn) increased with N level in the irrigation solution, whereas a negative impact was recorded for P, calcium (Ca), copper (Cu), and molybdenum (Mo) concentrations in both flower types
Summary
About 2% of known plant species are andromonoecious—a floral dimorphic sexual system in which an individual plant bears both hermaphroditic (bisexual) and staminate (male) flowers [1].Several evolutionary explanations for andromonoecy have been suggested. The resource reallocation hypothesis presumes that the development of male flowers has a lower energy cost than the development of bisexuals, and the energy saved by the mass production of staminate flowers might be reallocated to hermaphroditic flower development and fruit set [2,3]. Another hypothesis is that male flowers are more attractive to pollinating insects, and andromonoecy increases the chances of pollinators reaching these flowers and carrying the pollen [4]. Hand pollination of cashew stigmas with pollen from hermaphroditic or staminate flowers revealed a significant advantage for the male flowers in terms of grain germination
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