No abstract

The identification of readily measured traits that are associated with higher yields of field crops is important to plant breeders. The objective of this research was to determine if differences in grain filling rate and duration existed in rice (Oryza sativa L.) and if so, were these grain filling parameters correlated with other yield related components of the rice plant.Fifteen genotypes of rice were selected to represent a sample having diverse agronomic characteristics. Samples of panicles of the 15 genotypes were taken at weekly intervals for approximately 6 weeks during the grain filling period. The cubic polynomial model was found to closely fit the dry weight data (r2 ≥ 0.95 for all genotypes). Grain filling rate and duration as well as other grain filling parameters were determined from the model. Correlation between the grain filling parameters with yield components indicated that grain firing rate was more important than duration in this study. Grain filling rate, in turn, was positively and highly significantly correlated with actual panicle weight and 100‐grain weight and negatively correlated with panicles m‐2.

Spring wheat (Triticum aestivum L. em. Thell.) cultivars from various sources and different maturity classes were analyzed for responses to vernalization and photoperiod. Response measurements were days to heading, number of leaves on the main culm, and number of tillers at time of heading. Seven of 13 spring cultivars responded to vernalization as measured by reduced leaf number at heading, although differences were small. All 13 spring cultivars, plus a semi‐winter and a winter cultivar, headed sooner if vernalized, although the reductions (2 or 3 days) in some of them can probably attributed to slow development during vernalization. Tiller number at heading was reduced in cultivars responding to vernalization. Response to vernalization of spring types appeared unrelated to earliness of maturity under field conditions. All cultivars tested headed earlier with increasing photoperiods in a series of treatments from 9 to 17 hours. Early maturing cultivars responded least to lengthened photoperiods, and late‐maturing cultivars responded most. A highly significant interaction was obtained between the vernalization and photoperiod responses in one cultivar showing small responses to these individual treatments. However, photoperiod alone rather than vernalization appeared to be the primary factor controlling maturity in spring wheats.

IntroductionThe responses of plants to varying photoperiod has received much attention since GARNER and ALLARD (3, 4) first showed that flowering and fruiting of maniy plants is controlled by the relative length of day and night. Numerous species have been classified as "'short day" or "long day" on the basis of the day length required for maximum flowering and fruiting. Temperature also may influence the flowering responses of plants (13), and the two factors may show interaction (11).The experiments with Kentucky bluegrass (Poa pratensis L.) reported here were conducted primarily for the purposes of studying the physiological response of this species to management practices which might influence forage and seed production (9, 10). The formation of flowers in May and June has placed this species in the "long-day" class. However, EVANS and WATKINS (2) found that bluegrass plants produced inflorescenses in the spring regardless of length of day, and none was reported in the fall under day lengths ranging from 8.5 to 18 hours. Since plants are dependent upon their leaves for both the stimulus of photoperiod (5, 6) and reserve accumulations, any cultural treatments such as close grazing or clipping of Kentucky bluegrass could influence subsequent seed production, either through induction or through subsequent development of flowers and fruits. An interaction of nitrogen fertilization with photoperiod also was found in studies reported by BORTHWICK (1).

A study was made of possible relationships between alpha‐amylase activity (referred to as “activity”) and rice (Oryza sativa L.) seedling vigor, particularly as to stand establishment from water‐sown seeds. Relationships between activity and seedling weight (wt) during germination were noted for different cultivars and under different temperature and oxygen conditions.The r values for activity ✕ wt for ‘IR‐8’ and ‘Italica Livorno’ were highly significant (0.99 and 0.96 respectively) from the 3rd through the llth days of germination. These two cultivars differed widely in seed weight, enzyme activity, and seedling weight increases. The r value among 20 cultivars was 0.60, significant at the 0.05 level. The range in activity units was from 121.2 (for Italica Livorno) to 16.2 (for ‘Colusa’). A comparison of activity units at 30 C on rice germinated on moist blotters, under water, and in a N2 atmosphere showed that submergence had little effect on activity but the oxygen‐free atmosphere cut AU in half. These same conditions greatly suppressed seedling weights. Low temperatures (18 C) severely reduced AU and weight. It was concluded that alpha‐amylase activity was not an important limitation to seedling development of water‐sown rice under cold‐water conditions.

A laboratory method was devised for evaluating seedling vigor of rice (Oryza sativa L.) cultivars, hybrids, and segregating populations at sub‐optimal temperatures. Seeds of 20 cultivars of diverse origin were soaked in distilled water for 24 hours at 30 C and then germinated in the dark on moist blotters at 15, 18, 20, 25, and 30 C. Seedling height was used as the primary criterion for evaluation. Growth differences among cultivars, temperatures, and their interaction were highly significant. The same cultivars were evaluated in a field trial where mean days to emergence ranged from 9.4 to 17.7 with a mean of 12.9, and percentage emergence ranged from 22.0 to 87.5 with a mean of 57.4. The above two traits were components of an emergence index which ranged from 12.9 to 76.0 with a mean of 44.4. Correlation coefficients of laboratory seedling heights at five temperatures with days to emergence in the field ranged from ‐0.74 to ‐0.89, at the 1% level, with percentage emergence — from 0.56 to 0.69, at the 5% level, and with emergence index — from 0.75 to 0.81, at the 1% level. Results indicated that performance hi laboratory tests was a satisfactory indicator of field performance.

Floret sterility induced by low temperatures of 15 C or below at meiosis (10 to 15 days before heading) is a major factor in reducing yields of Oryza sativa, var. japonica, L. in California. The objective of this study was to reduce Sterility by manipulating genotypic environmental interactions. Field experiments employing differences in plant height, maturity, and water level were conducted at the Davis Rice Research Facility. Microclimatic studies were also conducted to determine temperature profiles within the canopy. Sterility was compared among nine cultivars with similar genetic origin but differing in plant height and maturity. Those that were short‐statured and/ or early‐maturing exhibited significantly less sterility than tall and late cultivars. All cultivars in a water depth study showed less sterility in deep water (15 to 25 cm) than in shallow water (5 to 15 cm). Mean differences were significant at the 0.05 level. The beneficial effect of earliness in reducing sterility was caused by the weather patterns of the rice‐growing region in the Sacramento Valley. The probability of receiving temperatures below 15 C at meiosis was considerably reduced as maturity was shortened. Increased water depth and decreased plant height reduced sterility by placing the panicle in closer proximity to water. Field water temperature at the coldest part of the night was usually 5 to 6 C warmer than air temperature. The microclimatic study demonstrated that absence of substantial nocturnal wind caused a temperature inversion at night between the mid‐canopy level (50 cm above soil surface) and the top of the canopy. Temperature also increased from mid‐canopy to water level because of the warming effect of the water. Thus mid‐canopy is the coldest part of the vertical profile in a rice field.

The effects of independent single genes for plant height, maturity, and pubescence on rice (Oryza sativa L.) seedling vigor in closely related, homozygous F~ lines were studied in laboratory and water-seeded field experiments. Laboratory seedling height, days to emergence, emergence percentage, emergence index, and 100-grain weight were measured. Mature plant height and maturity had no sig. nificant affect on laboratory seedling height. Pubescent lines as a group exhibited greater seedling vigor than glabrous lines in th e laboratory seedling height test, and emerged through the water sooner in the field test. However, several individual glabrous lines exhibited as much vigor as pubescent lines. Tall lines as a group showed a higher emergence percentage than semidwarf lines. There was a significant height × maturity × pubescence interaction for emergence percentage and emergence index. Semidwarf lines with seedling vigor equal to the tall parent were obtained. It appears that moderately high levels of seedling vigor can be attained in high yielding semidwarf rice cultivam.