Growth, Phenophases, Growing Degree Days Requirement and Yield of Rice Cultivars under Semi-arid Tropics

In India, rice occupies an area of 45.07 million ha with a production of 122.27 million tons and productivity of 2713 Kg/ha (Anonymous, 2023a). In Odisha, rice is cultivated in 4.03 million ha during kharif and rabi / summer seasons with a production of 8.73 million tons and productivity of 2173 kg ha^-1 (Anonymous, 2023b). Cultivar productivity is greatly influenced by genotype-environment interactions, which plays a key role in yield performance. (Rasyad et al., 2012; Jadhav et al., 2019; Kesh Hari  et al., 2023). Selecting a variety not suited to the region’s climate may result in reduced grain yield (Hussain et al., 2020; Panja Suraj  et al., 2024). By understanding the specific environmental factors in southern Odisha and their interaction with different rice genotypes helps in identifying varieties that are most likely to give high and stable yields. Moreover, region-specific studies can help in selecting rice varieties that are resilient to biotic and abiotic stresses prevalent in the region. This adaptability is key for mitigating risks and ensuring reliable productivity. However, the information regarding the suitability of the released varieties for southern Odisha is not available, an explorative study was conducted with 14 rice varieties during kharif season to find out suitable cultivars for the region targeting SDG goals 1,2, 4 and 15 of United Nations.
 

The maximum temperature varied from 28.2°C to 35.06^oC and the minimum temperature ranged from 18.57^oC to 26.5^oC. The sunshine hours ranged from 4.8 h/day to 11.0 h/day and relative humidity ranged from 83.57% to 89.71% and 59.29% to 80.42% in the 7:00 AM and 2:00PM, respectively. The total rainfall received during the crop growing period was 843 mm rainfall (Fig 1 and Fig 2).





 Among the tested cultivars, CR Dhan 319 yielded comparable to MTU 1010 and was significantly superior to others (Table 1). It recorded a higher number of panicles/m² than several cultivars and was comparable to MTU 1075, MTU 1061, CR 315, MTU 1010, Mohini, Pooja and Sowbhagya (Table 2). CR Dhan 319 also had superior panicle length, spikelet number and yield attributes, positively correlating with grain yield (Table 3). Longer-duration varieties (154 days) have shown improved yields, aligning with reports that the best yields come from 130-140 day varieties (Vergara, 1970; Satapathy et al., 2021), leading to their use for higher yields in some regions (Ishizuka et al., 1973).







Grain production, the ultimate outcome of growth and development, hinges on dry matter production during the ripening phase (Tanaka et al. 1974; Sagar et al., 2023). The higher dry matter production of the cultivar CR Dhan 319 (Table 1) helped to increase yield attributing characters; number of panicles per m2 (Table 1), spike lets per panicle, panicle length as compared to other cultivars which could result in higher grain yield than other cultivars (Table 2). These yield attributes had positive correlation with grain yield (Table 3) indication of increase in these parameters improved the grain yield of rice.

The different phenophases of the rice cultivars grown were identified in this experiment and days taken after transplanting was decided (Table 4). The GDD of different cultivars was estimated by taking in to consideration of standard procedure. The GDD at vegetative stage ranged from 530 to 1204, at reproductive stage 543 to 572 and ripening stage 461 to 545among different cultivars (Table 4). The GDD was higher at vegetative stage in long duration cultivars while it was higher at reproductive stage in short duration varieties. The total GDD from transplanting to harvesting was higher in case of long duration cultivars and less in short duration cultivars. Whenever the cumulative GDD were more, there was higher yield (Table 1) (Abhilash et al., 2017, Brar et al., 2011 and Sharma et al., 2011). There was an increase in rice grain yield with improvement in total GDD (Fig 1). It has been found that maximum grain yield in kharif was obtained at 2060 GDD beyond which there was decrease in yield.



 Analysis of correlation between grain yield and GDD showed significant positive correlation between GDD at vegetative stage while there was no relation at reproductive stage and negative significant relation at ripening stages (Table 3) and in long duration cultivars the vegetative stage duration was more compared to medium and short duration varieties (Table 4). The significant positive correlation between yield and GDD at vegetative stage contributed to higher grain yield in long duration cultivars as these had long vegetative period and accumulated higher GDDs (Table 3). The cultivar Marvel and CR Dhan 308 have given lower grain yield due to less accumulation of GDD from transplanting to vegetative and these cultivars matured early hence recorded lower yield as compared to medium and long duration cultivars.

 The reproductive and ripening stages were divided into five phenophases, with GDD varying across stages (Table 5). Short-duration cultivars (CR Dhan 308, Marvel 111) had higher GDD from reduction division to maturity, while CR Dhan 319, MTU 1075 and others recorded lower values. The optimum GDD for each stage was 120 (PI to young panicle), 245 (young panicle to reduction division), 178 (reduction division to anthesis), 113 (anthesis to ripening) and 365 (ripening to maturity). The correlation between GDD and grain yield at these stages was positive at reduction division to anthesis, anthesis to ripening and ripening to maturity stage indication of higher GDD at these stages increased the grain yield (Table 3)

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Through regression analysis, best fit curves were fitted between grain yield and GDD. At all stages, the polynomial curve of order 2 better fitted except in case of reproductive stage where 4^th order polynomial was better fitted.  The Regression analysis showed that the GDD at various phenophases and grain yield (Fig 3) had good agreement and indication that the variance in   grain yield a dependent variable is explained by the GDD an independent variable to the extent of 52 % at vegetative and 51% ripening stages (Table 6).




       
The grain yield was higher with increase in duration of the crop (Fig 4). Vergara  et al. (1966) indicated that in short-duration rice varieties, minimal carbohydrate accumulation, including starch and sugars, occurs during both the vegetative and reproductive stages.


   
At 90 DAT and harvest the dry matter production of CR Dhan 319 was comparable with MTU 1010 and significantly superior over all other cultivars (Table 1).  There are reports that differences have been observed in grain yield among genotypes having the same amount of dry matter due to differences in the utilization of photosynthates (Hayashi,1995). The biological yield of a cereal crop represents the total yield of plant tops and serves as a measure of the crop’s photosynthetic capacity (Yoshida, 1981). It is determined by the crop’s growth duration and the Crop Growth Rate (CGR) observed at various growth stages (Tanaka and Osaki, 1983).
 
The cultivars which had harvest index above 43% are MTU 1061, CR 315, MTU 1010, Mohini, Sowbhagya and CR Dhan 319 and other cultivars had HI less than 42%. There was higher HI in case of CR Dhan 315 and MTU 1010 besides other cultivars showed increasing yield trends and these increases were attributed to improvement in harvest index, which is associated with traits such as plant height, increase in biomass, or the combination of dry matter accumulation (Samonte et al., 1998).  Rice GHI values vary greatly among cultivars, locations, seasons and ecosystems thereby indicating the importance of this variable for yield simulation (Kiniry  et al.,2001). As the CR Dhan 319 had higher GHI which ultimately recorded higher grain yield over other cultivars.
     
 The variety MTU 1010 also recorded similar yield with that of CR Dhan 319 due to comparable yield attributes and dry matter production. The grain yield of MTU 1010 was significantly superior over CR 316, MTU 1064, CR315, CR Dhan 314, CR Dhan 308, Marvel 1011 and CR 313 cultivars due to increased growth and yield attributes as that of latter cultivars which ultimately resulted in higher yield. There was significant correlation between grain yield and yield attributes which indicates that the improved yield attributes in MTU 1010 resulted in higher yield. The yields of other cultivars are lower than above cultivar due to lower yield attributes there by lesser yield.

From these results it can be concluded that the cultivars CR Dhan 319 gives higher grain yield and net income among fourteen cultivars tested in southern Odisha. Further, for higher grain yield it is recommended to grow long duration cultivar having 145-150 days duration (sowing to harvest) with 2060 GDD Celsius (transplanting to maturity).

The authors declare that there is no conflict of interest related to this article.