Phenology, pollination and breeding system of Aegle marmelos (Linn.) correa (Rutaceae) from India

Abstract

Studies on reproductive biology are difficult but useful in species like Aegle marmelos (Linn.) Correa which is of considerable socio-economic importance and possess morphogenetic variation and qualities of wider adaptability to different soils. Cytology, phenology, pollination, breeding system and natural regeneration of wild and cultivated trees from India revealed the existence of diploid (2n = 18) and tetraploid trees (2n = 36) in Pachmarhi hills and only diploid trees in Punjab plains and Shiwalik hills. The diploid and tetraploid trees showed normal meiosis and high pollen fertility. Phenological events which included leaf fall, leaf emergence, floral bud break, flowering and fruiting are nearly the same in wild and cultivated trees. Natural pollen transfer in the species was highly efficient. Levels of fruit set following open pollination was quite high and is reduced considerably following hand pollination probably due to some injury caused to stigma during experiments. Inspite of synchronous nature of anther dehiscence and stigmatic receptivity, selfing in a flower was avoided due to herkogamy. Some selfing, however, occurred through geitonogamous mode as bagging of panicles yielded 12.21 ± 0.99 to 14.12 ± 0.91% fruit set. High pollen ovule ratio (9,250–10,600) indicated toward the obligate outbreeding nature. The species suited to insect and wind mode of pollination. High amount of air borne pollen grains deposited on glycerine smeared glass microscopic slides suggested towards the wind mode of pollination. Though flowers are dull coloured a variety of insects visited the flowers due to sweet fragrance and stamen/pollen as food reward. Among insect pollinators, honey bee (Apis dorsata) was the major and legitimate pollinator while the rest were either minor pollinators or mere visitors. Inspite of high fruit/seed set, natural regeneration through seeds was poor as fallen fruits were destroyed by fungal pathogens and white ants. The species also propagated vegetatively through coppices and root suckers. It lacks agamospermy as bagging of emasculated flowers yielded no fruit. It is inferred that ‘bael’ which lacks agamospermy reproduced successfully through gamospermy (xenogamy and geitonogamy) and vegetative mode (coppices and root suckers). We also concluded that tetraploid trees growing in the Pachmarhi hills with large sized fruits possessed better potentialities in horticulture if planted through root suckers or coppices.