In water yam (Dioscorea alata L.), bulbils are formed on the axil of their stems and have the potential as seeds for propagation. However, little is known about their growth and development or their dormancy. This research is aimed at obtaining the basic information concerning bulbil dormancy and the formation process in the water yam.
The effects of temperature on bulbil sprouting was examined and anatomical observations were carried out. Bulbil sprouting was promoted under high-temperature storage while inhibited under low-temperature storage, suggesting that the characteristic of bulbil sprouting is similar to that of the tubers in water yam, and the dormancy period is controlled by temperature. Anatomical observations of sprouting bulbils revealed apical buds with bud primordia in all of them at harvest, while observations during plant growth shown the formation of bulbils on the axil, with obvious bulbils developing 165 days after planting. In anatomical observation, no bulbils were observed at 135 DAP, and organs observed at this stage were thought to be axillary buds. Small globular tissues were then observed on the axil at 150 DAP, followed by obvious bulbils at 165 DAP, along with axillary buds. That is, the bulbils appeared in the endo-/eco-dormant phase, along with the development of axillary buds, suggesting a short period of endo-dormancy. The use of water yam bulbils as seeds for propagation, therefore, requires careful control of storage temperature and dormancy conditions.
Exploration of local citrus genetic resources grown on Ambon Island, Maluku, Indonesia was conducted in June and July 2014. Among the 28 accessions investigated, three accessions purchased at a local market were from Seram Island close to Ambon Island. The remaining 25 accessions were local citrus genetic resources grown on Ambon Island. According to the morphological traits, the citrus collected could be grouped into lime (Citrus aurantifolia), purut (C. hystrix), calamondin (C. madurensis), pummelo (C. maxima), sweet orange (C. sinensis), and mandarin (C. reticulata). Cleaved amplified polymorphic sequence (CAPS) analysis of the accessions was conducted, and precise accession identification was possible based on the results of CAPS analysis in conjunction with the morphological traits. The results of CAPS analysis revealed that genetic diversity exists in accessions with the same name on Ambon Island. The genotypes of some accessions resembled to lime, purut, calamondin, sweet orange, and mandarin were differed from those of control species. In contrast, genotypes of all four “Lemon Bali” accessions were identical to those of pummelo. These results indicate the individuality and diversity of citrus genetic resources grown on Ambon Island.
The relationship between nitrogen (N) absorption and growth in water yam (Dioscorea alata L.) is not clearly understood. A previous experiment suggested that water yam is able to grow under poor soil conditions regardless without nitrogen fertilization; however, the source of nutrition was not identified. This study aimed to identify the source of N and the percentage of plant N derived from atmospheric N2 (%Ndfa) under poor soil conditions. Experiments were carried out on Miyako Island, Okinawa Prefecture, Japan, from April 2014 to December 2015. In experiment 1, water yam growth was compared under urea application (N treatment) and without (control), while in experiment 2 urea (N treatment) or cow manure (CM treatment) application versus without application (control) was compared. N and CM treatment had a positive effect on growth and tuber yield. However, while yellowish leaves were observed in control plants, they grew until harvest, and tuber yield was similar between treatments. The δ15N values of the N- and CM-treated plants suggested that N was absorbed from the urea and cow manure; however, in the control plants, the N source seems to have been atmospheric. According to the result of δ15N value, it was suggested that water yam cultivated without N fertilizer absorbed 38.04% N from air.