Purpose: Canopy light interception and extinction play a crucial role in determining crop yield. Developing new rice varieties with improved canopy architecture along with modified intrinsic photosynthetic mechanisms will ensure the global food security. However, a comprehensive understanding of local rice varieties addressing on such avenues have not been reported. Hence, our pioneering experiments were carried out to elucidate such underlying properties among locally developed two elite rice varieties viz; At-362 and Bg 94-1 grown in the Ampara district of Sri Lanka. Research Method:The field experiment was carried out at the Agro Tech Park, Malwatta (7°20'N and 81°44'E altitude 16.0 m above sea level) between October 2019 to January 2020 implemented with Randomized Complete Block Design with four replicates. The Photosynthetically Active Radiation (PAR) distribution on the above and below canopy level was measured during the pre and post-anthesis stages. Then leaf stomatal conductance, chlorophyll fluorescence parameters and the chlorophyll content were also measured. At harvest, the final biomass produced were compared. Findings:The result revealed that variety At-362 had a higher Leaf Area Index (LAI) of 2.64 at pre anthesis and tend to decline at the latter part of their growth cycle. The striking feature was the extinction coefficient (k) seems to be much lower (0.47) in the At-362 variety than the Bg 94-1 (0.60) depicting that the former has produced vertical leaves (erect-leaf type) while the latter tends to produce horizontal leaf plans in the canopy. Hence, light attenuation was high and eventually, the bottom canopy layer received much lower PAR. Furthermore, LAI had a strong negative correlation with understory PAR indicating that the canopy architecture with an improved light interception will lead to permit more light penetration and utilization through the improved quantum yield efficiencies than the horizontal canopies. Hence significantly (p<0.05) improved above-ground biomass and panicle weight were observed in At-362.Originality/value: This experiment depicts that rice yield could be further improved through introgression of canopy architectural features along with improved photosynthetic traits.
Fall armyworm Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) (FAW) is one of the devastating polyphagous pests having a wide range of host plants that contribute substantial losses to crop cultivation. For such pests, temperatures exert a significant impact on biology, distribution, and abundance. Hence the present study was executed with the aims of evaluating the effects of different temperatures on the growth and development of fall armyworm. FAW larvae collected from the infested field and were reared in three different temperatures regimes viz. 25±1°C (T25), 30±1°C (T30) and 35 ±1°C (T35) incubator provided with 12:12 photo period. Life table and fecundity tables were calculated using growth parameters. The results indicated that the mean duration of each stage of lifecycle at three different temperatures were significantly different from each other. The accumulated mortality at the adult stage was 95%, 61% and 64% at T35, T30 and T25 respectively. The net reproductive rate (Ro) was 132.17, the average period of generation time (Tc) was less in T30 (32.31) with the daily finite rate of increase in number (λ) was 1.1702 females/female/day and a population doubling time of 3.004 days. Similarly, the intrinsic rate of natural increase in number (rm) was 0.1511 females/female/ day and hypothetical female population in the F2 generation was found to be higher at T30 (17468.20) thus the results indicated that T30 favors the growth and development of FAW compared to the other tested temperatures. Our findings could be useful for the implication in pest management and forecasting.
Maize (Zea mays L.) is one of the most widely cultivated cereal crops throughout the world and is extensively grown in Sri Lanka. Information on the photosynthetic, biomass and grain yield of local maize accessions are useful for plant breeding programs. However, due to the scarcity of such information, this study aimed to investigate the potentials of maize accessions to select the best performers utilizing the rank summation and selection index criteria. As the first step, the seeds from 14 maize accessions along with two varieties viz; Pacific-999 and Bhadra (control) were established in the field. The leaf-level photosynthetic and chlorophyll fluorescence traits were analyzed, while biomass and yield traits were obtained at harvest, by employing standard techniques. Our findings revealed that traits related to growth, photosynthesis, and biomass showed greater variations among the maize accessions tested. The number of days taken to 50% flowering (44d-60d), photosynthetic rates (19.7-30.45 μmol CO2 m−2 s−1), transpiration rates (2.45-4.52 mmol H2O m−2 s−1), water use efficiency (5.69-8.13 μmol CO2 mmol H2O-1), and maximum quantum yield (0.68-0.73) among the tested accessions. Additionally, the variations in biomass (111.0-459 g/plant) and final cob yield (38-232 g/cob) were also seen among the maize accessions. According to rank summation index analysis, the maize accessions SEU2, SEU16, SEU15, SEU9 and SEU10 were superior in terms of photosynthetic rates, biomass and yield compared exhibiting with the lowest RSI values of 71, 100, 101, 103 and 117, respectively, than the cv. Bhadra. Therefore, future crop development programs can make use of these five potential maize accessions identified through this study.
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