SUMMARYWhite or Guinea yam (Dioscorea rotundata), grown for its underground tubers, is an important food in West Africa. Progress in yam breeding is constrained by variable flowering behaviour, making hybridization difficult. Yam clones may be dioecious, monoecious or hermaphrodite with variable sex ratios. The proportion of plants that flower and the flowering intensity also vary with season and location. The objective of the present work was to investigate whether variation in flowering behaviour was related to factors determining rate of development (photoperiod and temperature through sowing date, location and year) or growth (cumulative solar radiation and temperature). Sex ratios, the proportion of plants that had flower buds and open flowers, and the number of flowers or spikes was recorded in one male (TDr 131) and one female (TDr 99-9) clone of white yam grown in the field in Nigeria at three locations and at different sowing dates. Clone TDr 131 was uniformly male flowering, while clone TDr 99-9 exhibited a number of sex types with gynoecious, monoecious and trimonoecious plants observed. The proportion of flowering plants was low in both clones, averaging 0·34 in clone TDr 131 and 0·13 in clone TDr 99-9. Day of vine emergence had a significant and contrasting effect on the proportion of flowering plants and on flowering intensity in the two clones. In clone TDr 131, the proportion of flowering plants and flowering intensity declined with later vine emergence at all locations (r=0·43–0·53; P<0·05), whereas in clone TDr 99-9 the proportion of flowering plants increased with later emergence (r=0·46, P<0·01). In clone TDr 131, this response was strongly associated with warmer temperatures (r=0·49–0·50; P<0·05) and greater cumulative radiation (r=0·85–0·93; P<0·001) between vine emergence and flowering, rather than photoperiod at vine emergence. This suggests that flowering behaviour in the male clone TDr 131 is strongly influenced by factors that affect growth rather than development. Clone TDr 99-9, on the other hand, exhibited no clear relations between flowering and growth or developmental factors, though the proportion of flowering plants and flowering intensity was greatest at planting dates close to the longest day and at temperatures of 25–26°C. This might suggest that flowering behaviour in clone TDr 99-9 is controlled by photothermal responses.
Dormancy is a mechanism that regulates the timing of sprouting (germination) of affected plant parts as well as ensures that the food quality of edible parts is maintained in storage until the following growing season. In yam, however, little is known about the control of tuber initiation or tuber dormancy. The objective of this study was to determine the effects of selected plant growth regulators (PGRs) on tuber initiation and dormancy, using an in vitro system. In two replicated experiments, 2-chloroethylphosphonic acid (ethephon, an ethylene source), abscisic acid (ABA) and gibberellin (GA 3 ) -and their inhibitors silver nitrate, fluridone and 2-chloroethyl-trimethylammonium chloride, respectively -were added at two concentrations to the culture medium prior to explant culture. Dates of micro-tuber initiation and sprouting (end of dormancy) and tuber number were recorded. In the control (no PGR) in Experiment 1, micro-tubers were initiated at the base of the stem after 176 days and sprouted 235 days later, that is 411 days after culturing. Most PGR treatments had only small effects (±30 days) on the duration of dormancy and the time of micro-tuber initiation. However, in GA 3 microtuber initiation occurred after 76 days, about 100 days earlier than in the control, whereas fluridone affected the position of micro-tubers and duration of dormancy. With fluridone treatments, tubers were found at the base of the stem (normal position) and on lower and upper nodes. Lower node tubers sprouted within 225 days of culturing compared with about 420 days after culturing at other nodal positions and in other PGR treatments. These data suggest an important role for ABA and gibberellic acid in yam micro-tuber initiation and the induction of dormancy. Ann Appl Biol 157 (2010) 203-212 No claim to original US government works 203 Annals of Applied Biology
Salinity is veritable issue in coastal lowlands of Niger Delta, due to salt water intrusion, and can reduce yield of lowland rice. Hybrid lowland rice cultivar (particularly FARO44; SIPI) are currently distributed and cultivated across Nigerian agroecological zones but the specific effect of salinity on these hybrid rice varieties is not well defined. This study seeks to determine the effect of sodium chloride (NaCl) on germination and seedling growth of FARO44 (SIPI). The study was a pot experiment, with 5 levels of sodium chloride (NaCl) concentrations (0, 1.0, 1.5, 3.0, and 5.0 dS cm -1 ). The seeds took about 30days to germinate in the control, as compared to other treatments. Germination was 42% in the control, 45% at 1.0 dS cm -1 and 34% at 5.0 dS cm -1 . A visual assessment for salt injury showed that the Control plants had normal growth of leaves and at 5.0 dS cm -1 NaCl, there was nearly normal growth of leaves but the tips of the leaves were whitish and rolled. Vegetative growth studies showed that the height to the first leaf in the control was 4.45m and the longest height to the first leave was recorded at 1.5 dS cm -1 NaCl. The tallest (38.7 cm) plants were observed at the 1.5 dS cm -1 NaCl treatment but it was statistically similar with other treatment expect in the control which had the lowest plant height (23.4 cm). The highest number of leaves was recorded at 1.5 dS cm -1 NaCl concentration, while lowest was recorded with 5.0 dS cm -1 NaCl. FARO44(SIPI) appears to tolerate NaCl of up to 1.5 dS cm -1 .
SUMMARYProlonged inability of yam tubers to sprout/germinate is associated with the expression of tuber dormancy, and the start of dormancy in tubers is linked to the onset of tuber formation. Although the plant hormone, abscisic acid (ABA) is known to regulate the onset and maintenance of dormancy in tubers, there are no known method(s) of inducing shoot growth (sprouting) on seed yam tubers that are harvested at 240 days after vine emergence or earlier. Therefore, this study was conducted to: (1) determine whether the absorption of fluridone, a reputed ABA inhibitor, prior to or during early seed yam tuber formation would induce sprouting, and (2) determine the effect of fluridone on early shoot growth. The study was a 2×4 factorial experiment arranged in a Completely Randomized Design (CRD) with eight treatment combinations replicated three times. Two species of yam with long dormancy durations were used: D. rotundata var TDr 131 and D. alata var TDa 98/01166; and three concentrations of fluridone were tested (30, 50, 100 µM). Young plants (69 days after vine emergence) of TDr 131 and TDa 98/01166 were grown in a coco coir medium hydroponics system using Hoagland's Nutrient Solution, with or without the test fluridone concentrations. In all fluridone treatments, most leaves of both species of yam had 30–90% of their surface bleached while the stems appeared purplish. In both Controls, all the newly formed seed tubers that were harvested at 90 and 104 days after vine emergence were dormant (devoid of any new shoots/sprouts). In contrast, over 70% of the seed tubers that developed in 30 and 100 µM fluridone had at least one new shoot, particularly in TDa 98/01166. The fluridone treatments did not significantly affect tuber weight or vegetative growth parameters like dimensions and number of leaves. This study has shown that the duration from vine emergence of the old tuber to sprouting of the new tuber can be reduced by more than half if young plants absorbed fluridone during early tuber development.
This study was conducted to determine the changes in dry matter (DM), free sugar (FS) and starch contents in the three yam (D. rotundata) tuber regions under two storage environmental conditions (natural light- yam barn, or and darkness). Three varieties of D. rotundata (alaako, Dodoro and Odo) were studied. The dry matter content of the Head region was the highest (28.6%), followed by the Middle (26.9%) and Tail (22.3%) regions. Change in dry matter content of the tuber is mainly due to rapid changes in the dry matter content of the Tail region over time. Storage environment significantly (P< 0.05) affected dry matter content of the three tuber regions at 8 and 16 weeks in storage (WIS). Head regions per variety were lower in dry matter when stored under Light than in the Dark at 8 WIS, while the reverse was the case for the Tail. This may relate to the release of endodormancy. By 16 WIS, when tubers stored under Light had well developed sprouts and those stored in the Dark only showed the first sign of sprouting, all Head regions had higher dry matter content under Light than in Dark storage. This may be due to the presence of sprouts. Storage environment did not significantly affect starch content at the various tuber regions. Head regions had higher percentage free sugar content under Light than Dark storage, and these effects were manifested between 8 and 16 WIS.
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