Photoperiod-sensitive Varieties Research Articles

Genetic variation in heading dates and phenological parameters of Myanmar rice

ABSTRACT Genetic variation in heading dates is essential for developing a rational rice cultivation program, optimizing irrigation practices, and advancing plant breeding in year-round irrigated environments. In this study, we investigated the heading dates of eight rice varieties with varying degrees of photoperiod sensitivity under natural field conditions by conducting year-round periodic sowing in 2019 in Nay Pyi Taw, located in the central region of Myanmar. We elucidated genetic differences in critical day length by observing the longest day length at 30 days before heading, which is likely to be the starting point for floral induction. We analyzed two phenological models: the conventional developmental rate (DVR) model and a modified model considering the critical day length. These analyses aimed to uncover the genetic differences in phenological parameters: temperature sensitivity, photoperiod sensitivity, and earliness among rice varieties. Incorporating the critical day length into the DVR model significantly improved its accuracy in predicting heading dates, particularly for photoperiod-sensitive rice varieties. The parameters derived from the 2019 data proved effective for predicting heading dates in 2018, especially for photoperiod-sensitive varieties. The genetic variation in critical day length and model parameters could be valuable for adapting rice cultivars to different seasons and determining yield and agronomic practices for varietal development programs. These findings contribute to a deeper understanding of rice phenology and the genetic basis for photoperiod sensitivity in Myanmar rice.

Growth Performance of Photoperiod-Sensitive Rice (Oryza sativa L.) Varieties in Different Soil Types under Rainfed Condition in Cambodia

In Cambodia, rice is predominantly produced in areas with rainfed lowland conditions where photoperiod-sensitive varieties are cultivated. A number of varieties have been released for rainfed lowland areas, and the rice grain yield has reportedly increased by approximately 12% over the past ten years. Moreover, great fluctuations in yield performance have been observed across different soil types of the rainfed ecosystems of Cambodia. Therefore, the present study aimed to analyze the grain yield and stability among ten popular varieties that were released for rainfed lowland ecosystems across the four different soil types in Cambodia in two years. The grain yield varied 566 g m−2 as the highest in clay soil and about 220 g m−2 as the lowest in sandy soil. A combined ANOVA revealed significant differences for the main effect of genotype, environment, and genotype-by-environment interaction (GEI) for all yield-related traits and grain yield per square meter. The principal component test results showed that the heterogeneity of grain yield was mainly attributable to the effect of environment, followed by the effect of genotype. In fertile conditions, a higher percentage of filled grains was supported by higher leaf N until the late stage with a wider flag leaf. In conditions of moderate fertility, larger numbers of panicles were supported by a higher percentage of productive culms with higher leaf N until the late stage. In conditions of poor fertility, a higher percentage of filled grains was supported by higher leaf N until the late stage, which is considered to be important for higher grain yield. The variety Phka Rumduol showed these preferable traits and produced higher yields in fertile to poor natural soil fertility conditions with moderate variation. This variety is considered to be more desirable and ideal due to its stability and higher grain yield. The other varieties, namely, Phka Mealdei, Phka Rumdeng, and CAR4, were identified as above-average yielders. Therefore, those varieties potentially may be recommended for cultivation in rainfed lowland rice ecosystems in Cambodia due to their high yields. CAR4 showed moderate variation at the same level as Phka Rumduol. From the point of stability, Phka Rumduol and CAR4 can be expected to excel.

Estimation of flowering time and its effect on grain yield of photoperiod sensitive varieties in rainfed lowland rice in Northeast Thailand

Flowering time of photoperiod sensitive varieties is an important determinant of grain yield of rainfed lowland rice, and is affected by the growing environment. The present study aimed to quantify variety specific flowering time response to photoperiod under irrigated conditions and demonstrate the usefulness of delay in flowering observed in rainfed lowland fields as an index of severity of water deficit affecting yield. Both irrigated on-station and rainfed lowland on-farm experiments were conducted with 4 popular photoperiod sensitive varieties in Northeast Thailand. The irrigated experiment was conducted with 12 sowing times throughout a year and flowering time was quantified with prevailing daylength and temperature. Among the 4 varieties, the minimum time to flowering varied from 68 to 77 days, and maximum daylength required for panicle initiation varied from 12 hrs 21 min to 12 hrs 39 min. Flowering time of all varieties was delayed in 3–4 sowings due to cold during vegetative stage; these sowings did not coincide with farmers’ common sowing time. On-farm flowering time and yield data were obtained from 108 crops grown under rainfed lowland conditions across 8 provinces in Northeast Thailand in 2013–2015, and were used for validating flowering time and grain yield simulation based on the sequential sowing experiment. Both curvilinear and linear equations to estimate time to flowering from sowing time gave a similar result. Delay in flowering due to water deficit observed on-farm was estimated as the difference between the observed on-farm and simulated flowering time under irrigated conditions, and the estimated delay was related to grain yield reduction due to water deficit. It is concluded that simulated flowering time under irrigated conditions together with observed flowering time in farmer’s fields can be used to determine flowering delay under rainfed conditions, and the delay is an indication of the severity of water deficit reducing yield. Extension material may be developed in which estimated flowering time of key varieties under well-watered conditions may be tabulated for various sowing times and locations in the region, and then farmers can determine delay in flowering and likely yield reduction for their own and neighboring crops.

Variation of Anthocyanin, Phenol, and Antioxidant Capacity in Straw among Rice Varieties and Growing Locations as a Potential Source of Natural Bioactive Compounds.

This study evaluated the variation in bioactive compounds (anthocyanins, phenols, and antioxidants) among 22 rice varieties in the same growing locations and among four varieties collected from eight different provinces in Northern Thailand. Wide variation in anthocyanins, phenols, and antioxidant capacity was established, ranging from 1.6 to 33.0 mg/100 g, 249.9 to 477.7 mg gallic acid/100 g, and 0 to 3,288.5 mg trolox equivalent/100 g, respectively. The highest straw anthocyanin and phenol concentrations were found in KDK (a traditional photoperiod-sensitive variety with purple pericarp and leaves) and K4 (an advanced, photoperiod-insensitive variety with purple pericarp and leaves), while the highest antioxidant capacity was found in KH CMU (an improved traditional photoperiod sensitive variety with a purple pericarp and green leaves) and K4. The variation of the bioactive compounds was also found in the same variety grown at different locations, e.g., the KDMl105 grown in Prayao province had a straw anthocyanin concentration higher than when grown in Mae Hong Son province. The effect was also observed in phenol content and antioxidant capacity when the same rice variety was grown across various locations. A significant correlation between total phenol and antioxidant capacity was observed across rice varieties and growing locations but was not found between anthocyanin and antioxidant capacity. This study found that the bioactive compounds in rice straw varied among rice varieties and growing locations. Straw phenol acts as a major antioxidant that can be used as a characteristic for the selection of rice varieties with high antioxidant capacity for use at the industrial scale for the processing of food, pharmaceuticals, and medicinal products.

Genetic analysis and QTL mapping of growth period traits and plant height traits in soybean recombinant inbred lines from Dongnong 47 × PI 317334-B

High and stable yield is the main goal of soybean genetic improvement. In this study, association analysis was used to detect the quantitative trait loci (QTL) for the plant height, and soybean growth period using 182 SSR markers in the RIL population of 136 F4:8 lines, which developed from a cross between photoperiod-insensitive cultivar ‘Dongnong 47’ and photoperiod-sensitive variety PI317334–B. The results showed that 33 QTLs related to soybean growth period and plant height traits were detected by compound interval mapping, and were located on 12 linkage groups including N, C1, C2, J, D1a, B2, E, G, A2, O, L, I, with the contribution rate of 7.85–33.84%. These QTL loci and linkage markers related to soybean photoperiod sensitivity, would be helpful to identify key genes that control soybean photoperiod sensitivity, and provide an important basis for the breeding of new photoperiod-insensitive soybean varieties based on molecular design breeding.

Combined transcriptome sequencing reveals the photoperiod insensitivity mechanism of oats

Avena sativa L. is the most important cultivated oat species worldwide. Although photoperiod-insensitive oat varieties exist, the molecular mechanisms underlying their photoperiod sensitivity are poorly understood. This study investigated the effects of day length on the fioral transition of oats and the mechanisms underlying oat photoperiod insensitivity. Photoperiod-sensitive and photoperiod-insensitive varieties, including gp012, were used in shading experiments, and the developing leaves and main shoot apices (MSAs) of the HONGQI2 and gp012 varieties were used for sequencing. Leaves and MSAs were collected in 2016, and their transcriptomes were sequenced. The photoperiod-insensitive varieties headed under both short-day and long-day conditions, while the photoperiod-sensitive varieties headed only under long-day conditions. A total of 60673 transcript sequences were obtained, 7932 of which were differentially expressed; 3194 and 4738 transcripts were differentially expressed in the leaves and MSAs, respectively. A total of 25793 transcripts were classified into 123 pathways based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. The carbon metabolism pathways were dominant, followed by ribosome and protein processing in the endoplasmic reticulum. In addition, 203 transcripts were classified into the circadian rhythm pathway. Compared with the expression of pseudo-response regulator protein 37 (PRR37) in photoperiod-sensitive varieties, that in photoperiod-insensitive varieties was upregulated. Among the differentially expressed transcripts (DETs), 8 MADS-box genes were identified. PRR37 is a key regulator of oat photoperiod insensitivity. The obtained transcriptome dataset may provide a reference for analyzing oat transcript expression, and the results should be used as a reference for oat breeding and production.

English

In Sub-Saharan Africa, Genotype-Environment interaction plays a key role in formulating strategies for crop improvement. Multi-location trials have created enabling structure to determine varieties yield performance and stability. Crop modeling led to prediction of long-term and spatial effects of climate variability. Three improved varieties were compared to three landraces. Optimum cultivation areas minimizing the risk of crop failure were delineated by comparing predicted flowering dates and end of rainy seasons. Agronomic values were determined in trials from three climatically different zones in 27 farms. Yield stability was determined using linear regression depending on each environmental mean and the AMMI model. Photoperiod sensitive varieties have wider optimal cultivation areas whereas early-maturing varieties (photoperiod insensitive) are subjected to strong constraints on sowing date. In low productivity conditions, landraces and improved varieties are not distinct. As the environmental cropping conditions increase, improved lines become significantly superior to landraces. Photoperiod insensitive landrace is subservient to climate conditions of its area of origin and its productivity drops sharply when moved to a wetter area. Varieties studied combined productivity and stability traits. These findings are important steps toward breeding climate resilient varieties for meeting the challenges of climate smart agriculture and sustainable intensification. Key words: Mali, sorghum, GxE, photoperiodism, climate change, yield stability. &nbsp

Prospecting for Energy-Rich Renewable Raw Materials: Sorghum Stem Case Study.

Sorghum vegetative tissues are becoming increasingly important for biofuel production. The composition of sorghum stem tissues is influenced by genotype, environment and photoperiod sensitivity, and varies widely between varieties and also between different stem tissues (outer rind vs inner pith). Here, the amount of cellulose, (1,3;1,4)-β-glucan, arabinose and xylose in the stems of twelve diverse sorghum varieties, including four photoperiod-sensitive varieties, was measured. At maturity, most photoperiod-insensitive lines had 1% w/w (1,3;1,4)-β-glucan in stem pith tissue whilst photoperiod-sensitive varieties remained in a vegetative stage and accumulated up to 6% w/w (1,3;1,4)-β-glucan in the same tissue. Three sorghum lines were chosen for further study: a cultivated grain variety (Sorghum bicolor BTx623), a sweet variety (S. bicolor Rio) and a photoperiod-sensitive wild line (S. bicolor ssp. verticilliflorum Arun). The Arun line accumulated 5.5% w/w (1,3;1,4)-β-glucan and had higher SbCslF6 and SbCslH3 transcript levels in pith tissues than did photoperiod-insensitive varieties Rio and BTx623 (<1% w/w pith (1,3;1,4)-β-glucan). To assess the digestibility of the three varieties, stem tissue was treated with either hydrolytic enzymes or dilute acid and the release of fermentable glucose was determined. Despite having the highest lignin content, Arun yielded significantly more glucose than the other varieties, and theoretical calculation of ethanol yields was 10 344 L ha-1 from this sorghum stem tissue. These data indicate that sorghum stem (1,3;1,4)-β-glucan content may have a significant effect on digestibility and bioethanol yields. This information opens new avenues of research to generate sorghum lines optimised for biofuel production.

Functional analysis of GmCPDs and investigation of their roles in flowering.

The onset of floral development is a pivotal switch in the life of soybean. Brassinosteroids (BRs), a group of steroidal phytohormones with essential roles in plant growth and development, are associated with flowering induction. Genes involved in BR biosynthesis have been studied to a great extent in Arabidopsis, but the study of these genes has been limited in soybean. In this study, four CPD homologs (GmCPDs) catalyzing BR synthesis were isolated from soybean. Transcripts were mainly confined to cotyledons and leaves and were down-regulated in response to exogenous BR. Bioinformatic analysis showed strong sequence and structure similarity between GmCPDs and AtCPD as well as CPDs of other species. Overexpression of GmCPDs in an Arabidopsis BR-deficient mutant rescued the phenotype by restoring the biosynthesis pathway, revealing the functional roles of each GmCPDs in. Except for the rescue of root development, leaf expansion and plant type architecture, GmCPDs in expression also complemented the late flowering phenotype of Arabidopsis mutants deficient in CPD. Further evidence in soybean plants is that the expression levels of GmCPDs in are under photoperiod control in Zigongdongdou, a photoperiod-sensitive variety, and show a sudden peak upon floral meristem initiation. Together with increased GmCPDs in expression in the leaves and cotyledons of photoperiod-insensitive early-maturity soybean, it is clear that GmCPDs in contribute to flowering development and are essential in the early stages of flowering regulation.

Review of Flowering Control in Industrial Hemp

Hemp (Cannabis sativa L.) is a dioecious annual that commences its reproductive cycle when photoperiods are shorter than a critical length. Photoperiod-sensitive varieties grown in low latitudes with short-day lengths tend to produce early flowering, short plants affecting the yield and quality of the fiber. The photoperiodic sensitivity of the crop could be controlled by the activation or deactivation of genes triggered by the change in light duration perceived by photoreceptive pigments. The sexual dimorphism of Cannabis is genetically determined by the XY chromosomal mechanism although sexual morphology is primarily a result of endogenous plant growth regulator levels that fluctuate in response to environmental variables. Occurrence of occasional hermaphroditic flowers and monoecious plants are probably the result of these fluctuations. Understanding the mechanisms of photoperiodicity and sexual inheritance contributes to advances in breeding and crop management that may underpin the expansion of the commercial cultivation of the crop in nontraditional agroecological domains.

Yield gap analysis and the effect of nitrogen and water on photoperiod-sensitive Jasmine rice in north-east Thailand

Yield constraint analysis using a combination of experiments and crop growth models has been useful for quantifying the relative role of yield-limiting factors, and for prioritizing management interventions aimed at increasing the yields of non-photoperiod-sensitive rice grown under rainfed conditions. The use of a systems approach for photoperiod-sensitive varieties is constrained by the lack of crop growth models that can simulate the varieties’ photoperiod response. This study used data from the literature, from a controlled-growth experiment, and from multi-location field experiments to determine the photoperiod-sensitivity parameters of Jasmine rice grown in north-east Thailand, and incorporated these in the ORYZA2000 model. Next, the model was used to analyse yield gaps by comparing yields in farmers’ fields with the simulated attainable yields with an adequate N supply (60 kg ha −1) under irrigated conditions. The ORYZA2000 model adequately simulated growth, development, and yield of Jasmine rice over a 0–150 kg N ha −1 range under irrigated and normal to above-normal rainfall conditions. The simulated attainable yields ranged from 3.47 to 5.96 Mg ha −1. A simulated yield gap of 1.76 Mg ha −1 (41%) currently exists in rainfed rice farmers’ fields. Yield gaps could be substantially reduced by 1.48 Mg ha −1 (34%) through improved N-management practices. The yield gap caused by water limitation was small (0.02 Mg ha −1, <1%) during the study period, when rainfall was normal to above normal. The large yield gap beyond the farmers’ current fertilizer level suggests considerable scope for increasing yields through site- and time-specific nutrient management. A long-term simulation study including years with rainfall below normal is needed to comprehensively quantify yield gaps caused by water limitation. Such long-term simulation is hindered by the lack of long-term groundwater depth measurements.

Evaluation Of Okra Cultivars And Breeding Lines For Agronomic Traits In Umudike In Southeastern Nigeria

Six (6) genotypes comprising two (2) cultivars and four (4) breeding lines of Okra (Abelmoschus esculentus (L) Moench) were studied in a randomized complete block design with three (3) replicates to determine their performance under Umudike environmental conditions in 2002 and 2003 cropping seasons. With respect to fresh pod yield, all the genotypes performed very well in both years, although the breeding lines performed better than the two (2) varieties. Breeding lines LD88/1-8-16-2 and LD88/1-8-13-2-4 recorded fresh pod yields of 3.6 and 3.2 t/ha in 2002, 3.5 and 3.3 t/ha in 2003 respectively, which are well above the fresh pod yields recorded for Okra in the tropics. The early maturing Okra genotypes used in the present study with 3 to 4 months duration present a possibility of growing two crops of Okra (early and late croppings) in one year, unlike the indigenous photoperiod sensitive varieties with eight to nine months duration. Keywords: Okra, cultivars, breeding lines, and Agronomic traitsGlobal Journal of Agricultural Sciences Vol. 7 (1) 2008: pp. 11-15

Modeling the dependence of the crop calendar for rain-fed rice on precipitation in Northeast Thailand

Rain-fed lowlands are major agricultural ecosystems used for rice production in Northeast Thailand. Developing a tool to assess the effects of variable water conditions on the regional scale yield is also important to predict the effects of climate change on food supply. To estimate regional yields, we need a simple but accurate measure of the crop calendar (i.e., the distribution of planting dates), which has a strong influence on grain yield. In this article, we modeled the dependence of the crop calendar on rainfall patterns based on a survey of the region’s farmers as a part of an effort to provide a stronger basis for regional yield estimates. Our survey, conducted in 11 provinces for 2 years, confirmed the existence of large windows for sowing and transplanting versus narrow windows for heading and harvesting for rain-fed lowland rice culture in all the provinces. Variable water, soil, and toposequential conditions in the paddy fields were responsible for the large sowing and transplanting windows, whereas the use of photoperiod-sensitive varieties explained the narrow windows for heading and harvesting. The crop calendar was well expressed as a function of cumulative precipitation from June onward. When the crop calendar model was combined with a simple phenology-based model that uses growing degree-days adjusted by a day-length factor, we could estimate the rice crop calendar under rain-fed lowland conditions with acceptable accuracy. The model described in this article will be combined with a crop growth model to improve regional yield estimates for rain-fed lowland rice.

Minimising cold damage during reproductive development among temperate rice genotypes. I. Avoiding low temperature with the use of appropriate sowing time and photoperiod-sensitive varieties

Multiple-sown field trials in 4 consecutive years in the Riverina region of south-eastern Australia provided 24 different combinations of temperature and day length, which enabled the development of crop phenology models. A crop model was developed for 7 cultivars from diverse origins to identify if photoperiod sensitivity is involved in determining phenological development, and if that is advantageous in avoiding low-temperature damage. Cultivars that were mildly photoperiod-sensitive were identified from sowing to flowering and from panicle initiation to flowering. The crop models were run for 47 years of temperature data to quantify the risk of encountering low temperature during the critical young microspore stage for 5 different sowing dates. Cultivars that were mildly photoperiod-sensitive, such as Amaroo, had a reduced likelihood of encountering low temperature for a wider range of sowing dates compared with photoperiod-insensitive cultivars. The benefits of increased photoperiod sensitivity include greater sowing flexibility and reduced water use as growth duration is shortened when sowing is delayed. Determining the optimal sowing date also requires other considerations, e.g. the risk of cold damage at other sensitive stages such as flowering and the response of yield to a delay in flowering under non-limiting conditions. It was concluded that appropriate sowing time and the use of photoperiod-sensitive cultivars can be advantageous in the Riverina region in avoiding low temperature damage during reproductive development.

Does panicle initiation in tropical sorghum depend on day-to-day change in photoperiod?

Sorghum is known as a short day plant requiring short photoperiods (PP) to flower. However, in field experiments based on monthly plantings reported elsewhere, panicle initiation took place during long days as well as during short days even for highly photoperiod-sensitive varieties thought to be of the absolute type, or was particularly early for the sowings in September, well before days were shortest. In order to investigate these contradictory results, three tropical sorghum varieties of different photoperiod sensitivity were planted monthly in Mali and the dates of panicle initiation (PI) were recorded. The results indicate that the common concepts of a gradual (linear, or quantitative) response of photoperiod-induced phase (PIP) to PP at PI (PPi) (case of the variety Sariaso 10) or a threshold-type response (hyperbolic, or absolute; cases of CSM 335 and IRAT 174) could be reproduced for the sowing dates falling into the wet season (May–October), but did not describe adequately crop behaviour during the remaining months of the year. The same varieties were tested in controlled environments with four differential PP treatments composed of three different initial PP (12 h 15 min, 12 h 00 min and 11 h 45 min) and two opposite rates of day length change (±1 min/day). Thus after 15 days, two pairs of treatments with opposite day length changes reached the same average PP (12 h 07 min and 11 h 52 min) and after 30 d, another pair reached a similar average PP (12 h 00 min). In 2001, 2 varieties reached PI earlier under decreasing days and the same average PP, but no such additional effect of the rate of change of PP was observed in 2002. Modelling exercises showed that field variation in the duration to PI was better explained with rate of change of PP than with absolute PP observed during PIP, and best with a combination of both factors in an additive model. It is concluded that in tropical sorghum, floral induction is strongly associated with a negative rate of change of day length in the field, and under certain circumstances under controlled conditions, but more evidence is needed to ascertain the capability of sorghum to sense the rate of change of PP before a definite model can be formulated.

Mapping quantitative trait loci for flag leaf senescence as a yield determinant in winter wheat under optimal and drought-stressed environments

The timing of flag leaf senescence (FLS) is an important determinant of yield under stress and optimal environments. A doubled haploid population derived from crossing the photo period-sensitive variety Beaver,with the photo period-insensitive variety Soissons, varied significantly for this trait, measured as the percent green flag leaf area remaining at 14 days and 35 days after anthesis. This trait also showed a significantly positive correlation with yield under variable environmental regimes. QTL analysis based on a genetic map derived from 48 doubled haploid lines using amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers, revealed the genetic control of this trait. The coincidence of QTL for senescence on chromosomes 2B and 2D under drought-stressed and optimal environments, respectively, indicate a complex genetic mechanism of this trait involving the re-mobilisation of resources from the source to the sink during senescence.

Effects of planting date, intensity of tiller separation and plant density on the yield of transplanted rice

Experiments were conducted in Bangkok clay soil to investigate the influence of planting date, tiller separation and plant density on the yield and yield attributes of parent and clone plants of two transplanted rice varieties. The 15 July transplanting of mother crop and collected vegetative tillers and retransplanting on 15 August showed significantly high grain yield (3·8 t/ha). The photoperiod-insensitive variety RD23 gave higher yield (3·8 t/ha) than the photoperiod-sensitive variety KDML105 (3·0 t/ha). Tiller separation up to 4 tillers/hill did not adversely affect the mother crop. Vegetative tillers transplanted with 2–4 tillers/hill gave a similar yield as the mother crop in both the seasons. Vegetative tillers gave a higher yield than nursery seedlings transplanted on the same date. The yield components, i.e. weight of 1000 grains, grains/panicle and per cent filled grains, showed better responses with early transplanting of KDML105 in the mother crop and vegetative tillers except for panicle number and panicle length of vegetative tillers with RD23. The results suggest that in some flood-prone lowlands, where the transplanted crop is damaged by natural hazards, vegetative propagation using tillers separated (maximum 4/hill) from the previously established transplanted crop is beneficial for higher productivity.

Varietal screening of compatibility types revealed in F1 fertility of distant crosses in rice.

Reproductive barriers between distant groups of rice are anticipated to be overcome through a systematic use of widely compatible varieties in breeding programs. For this purpose a total of 74 varieties were screened for compatiblity types in terms of F1 fertility by crossing them to one each of indica and japonica testers. The compatibility of a variety to a tester was rated by pollen and spikelet fertility of the F1 hybrid. The pollen fertility of more than 90 percent and the spikelet fertility of 75-80 percent were rated normal. The compatibility tests showed that the pollen fertility is independent of the spikelet fertility. Therefore, each variety was inspected for four fertility scores, namely, the pollen and the spikelet fertility in each cross to an indica and a japonica tester. Out of 24 Indonesian upland varieties, 15 showed normal pollen fertility with both testers, and normal spikelet fertility with a japonica tester, but gave remarkable spikelet sterility with an indica tester. Six showed semi-sterility in all the four scores. Only one variety, Padi Bujang Pendek revealed normal fertility in all the four scores. The remaing two seemed to belong to an exceptional type. A total of 27 Aus varieties showed many types of compatibility including six varieties of indica type and five of japonica. Five varieties revealed sterility in all the four scores. Only two, Aus 373 and Dular seemed to be widely compatibe. The remaining nine were not classified into any difinite categories. In the test of 15 varieties which are identified tolerant of salinity, drought or peat soil, ten of strongly photoperiod-sensitive varieties were classified into typical indica rice. Two photoperiod-nonsensitiwe varieties were clearly identified to be japonica. In additional tests of some varieties which are notable from previous works, Calotoc, CPSLO 17 and Ketan Nangka were confirmed to be widely compatible. The screening results indicate that the Aus group of rice is a complex of various compatibility types, while a majority of Indonesian upland rices seemed to be of a type which is closer to japonicas rather than iledicas. Only a few varieties were identified as the wide-compatibility type, contrary to the expectation based on earlier works. It was discussed that the upland cultivation has permitted the Aus group to preserve the diverse compatibility types, while photoperiod-sensitive lowland varieties are predominantly of iledica type.

Comparative Potential Yields of Rice Varieties in the Australian Tropics

SummaryDuring the wet summer season of northern tropical Australia higher yields were attained by introduced weakly photoperiod-sensitive short-duration rice varieties than by locally-bred strongly photoperiod-sensitive varieties resembling traditional tropical indicas. There was no clear relationship between growth durations and yields. Dry season yields were lower, associated with shortened durations (especially of the reproductive phase) and lower cumulative radiation totals in the late phases of growth. Dawn, a variety of U.S. origin imported from the Philippines, outyielded all other varieties. In both wet and dry seasons yields depended largely on panicle weights, which in turn depended on high seed numbers per panicle. Individual seed weights were of less importance. The results tended to confirm a prior interpretation of climatic data, i.e. that there is no environmental factor limiting wet season yields in the region to levels below those obtained elsewhere in the tropics, provided the crop receives a high standard of care and attention.