Screening of rice cultivars for aroma at various growth stages under different dates of sowing in Konkan conditions

Introduction

Rice (Oryza sativa L.) is the staple food crop for over half of the world's population, with Asia contributing to about 90% of global production and consumption (Dubey et al., 2017) [2] . Among various types, aromatic rice holds a premium place due to its unique fragrance, taste, and market value. The aroma in rice is governed by genetic and environmental interactions, primarily influenced by climatic conditions during the growth period. Aromatic rice has huge demand both for national and international trade (Dutta et al. 2002) [3] . The Konkan region of Maharashtra, India, it holds significant cultural and economic importance. In Konkan, as in many rice-consuming regions, aroma plays a vital role in consumer acceptance, driving preference and often commanding premium prices. Aromatic rice varieties, with their desirable aromas described as floral, nutty, or popcorn-like, enhance the eating experience and are highly sought after in both domestic and international markets. Consequently, aroma is a key trait targeted in rice breeding programs. The expression of aroma in rice is a complex phenomenon influenced by both genetic and environmental factors. While a cultivar's genetic makeup determines its inherent potential for aroma production, environmental conditions during growth, as well as post-harvest handling practices, can significantly modulate aroma intensity and quality. Understanding this crucial interplay between genotype and environment is essential for developing stable and highyielding aromatic rice varieties suited to specific agro-climatic zones, such as the unique conditions of the Konkan region. Identifying high-yielding aromatic varieties adapted to these local conditions is crucial for improving livelihoods and meeting market demands. This study addresses the need for systematic screening of rice cultivars for aroma, considering the influence of growth stage and sowing date, which are known to affect aroma compound development. Specifically, this research aims to identify the most suitable aromatic rice varieties under Konkan conditions and to determine the optimal sowing dates for retaining aroma in selected varieties.

Materials and Methods

Fifteen aromatic rice genotypes (Table 1) were evaluated at the Research Farm, Department of Agricultural Botany, College of Agriculture, Dapoli, during the 2019-2020 cropping season. Dapoli is located in the sub-tropical, highrainfall zone of the Konkan region. The experiment followed a Randomized Block Design (RBD) with three replications and six sowing dates (Table 2) (D1: 30 th May, D2: 20 th June, D3: 10 th July, D4: 1 st October, D5: 20 th October, D6: 10 th November). 21 day old seedlings were transplanted at a spacing of 20 x 15 cm. Standard agronomic practices were followed throughout the growing period. Aroma was determined qualitatively by using the method as described by Sood and Siddiq (1986) [7] . Aroma was assessed at three growth stages (seedling, flowering, and maturity) and in cooked rice using sensory evaluation. A panel of five trained individuals evaluated the aroma, assigning scores as follows: NS (Non-scented), MS (Mildly scented), and SS (Strongly scented). Data were analyzed using ANOVA to determine significant differences between genotypes and treatments.

Results

Aroma scores recorded at different growth stages and sowing dates are presented in Tables 3,4, 5 and 6.

Seedling Stage Aroma

The data of aroma score recorded by the sensory method of all the fifteen genotypes over six environments are given in table 3. This table showed that the genotype PR-115 had strong scent during D1 to D4 environments where as mild scent during D5 and D6 environments. Genotype BM-4 and Pawana showed the mild scent during all the six environments. Remaining all twelve did not show the scent in any date of sowing when tested as seedling stage.

Flowering Stage Aroma

The data of leaf aroma score recorded by the sensory method of all the fifteen genotypes over six environments are given in table 4. The genotype PR-115 and BM-4 had strong scent during all environments. Remaining all thirteen genotype showed the mild aroma during all environments at the time of flowering stage.

Maturity Stage Aroma

The data pertaining to leaf aroma score recorded by the sensory method of all the fifteen genotypes over six environments are presented in table 5. This table indicated that the genotype PR-115 found the strong scent during all the environments. The genotype Ghansal showed the mild aroma only during D1 environments where as Basmati-376 did not show the aroma at D1 and D2 environments but showed the mild aroma for remaining D3 to D6 environments. The genotype Botvel, Ambemohar, Chimansal, Basmati-1017 and Super Basmati did not show the scent for all environments. The genotype BM-4, Indrayani, Pawana, Bhogavati, Kothmirsal, Basmati-386 and Basmati-370 showed the mild aroma for all environments at the maturity stage. At maturity, aroma profiles diversified. PR-115 remained strongly scented (SS). Eight genotypes were mildly scented (MS), and six were non-scented (NS). Ghansal showed mild scent only at D1, while Basmati-376 was non-scented in D1 and D2 but mildly scented from D3 to D6, highlighting the impact of sowing date.

Cooked Grain Aroma

The data for grain aroma recorded by the sensory method after cooking for all the fifteen genotypes over six environments are given in table 6. This table indicated that PR-115 had strong aroma during all the environments. The genotype Indrayani, Bhogavati and Basmati-386 did not show the aroma at D1 environments however showed the mild aroma in all the environments. Genotype Ghansal showed the mild aroma only during D1 environments but did not shows the aroma for remaining environments. The genotype BM-4, Pawana, Kothmirsal and Basmati-370 showed the mild aroma for all environments. The genotype Botvel, Ambemohar, Chimansal, Basmati-376, Basmati-1017 and Super Basmati did not find the aroma after cooking of rice grain. Cooked grain aroma showed similar trends to the maturity stage. PR-115 maintained its strong scent (SS). Seven genotypes were non-scented (NS), and seven were mildly scented (MS). Indrayani, Bhogavati, and Basmati-386 were non-scented at D1 but mildly scented from D2 onwards. Ghansal was mildly scented at D1 but non-scented in later sowings, further emphasizing the combined influence of genotype and environment.

Discussion

This table showed that PR-115 genotypes had strong scent during all the four stages i.e. seedling, flowering, maturity and after cooking as well as during all the six sowings followed BM-4 showed the mild scent during seedling, maturity and after cooking, whereas it had strong scent during flowering stage. All the fifteen genotypes showed the mild to strong scent during flowering stage in all the six sowing environments, however only eight genotypes viz., BM-4, Indrayani, Pawana, Bhogavati, Kothmirsal, Basmati-376, Basmati-386 and Basmati-370 showed mild to strong aroma during maturity stage in all the six sowing environments. Some of the aromatic rice varieties are loosing their aroma during growth stages from flowering to maturity stages. This might be due to increasing the temperature at the time of flowering. Sensory methods of aroma detection are not suitable for large number of samples because senses vary from person to person and physical damage in nasal passages may occur due to direct exposure with chemicals during smelling. These results are in resemblance with the results obtained by Hien et al. (2006) [5] . Different research worker used the sensory method for evaluation of aroma at various growth stages. Genetics, growing conditions, and post-harvest handling are factors which have been shown to affect the aroma and flavour of rice (Champagne, 2008) [1] . Rice aroma quality also highly depends on the cultivation process along with environmental conditions like temperature, soil type, abiotic stress, water, CO 2 light, salinity, shading the duration and conditions of storage, the time of harvest (Itani et al. 2004; Mo et al. 2018) [4,6] . The observed variation in aroma among rice cultivars highlights the importance of genotype selection for improving rice quality in the Konkan region. The significant increase in aroma intensity at the flowering stage aligns with the known accumulation of volatile compounds during reproductive development. The influence of sowing date on aroma suggests a strong genotype-environment interaction. Variations in temperature, humidity, and rainfall associated with different sowing dates likely affect the biosynthesis of aroma compounds. PR-115's consistent strong aroma across environments suggests its potential stability and suitability for Konkan. The fluctuating aroma profiles of other varieties indicate their sensitivity to environmental changes. The absence of aroma in some genotypes at specific growth stages or sowing dates might be related to their genetic makeup or their ability to adapt to the fluctuating environmental conditions during the cropping season.

Conclusion

This study identified PR-115 as a consistently strongscented cultivar suitable for the Konkan region. The research also demonstrated the significant influence of growth stage and sowing date on aroma expression in rice. These findings can assist farmers in selecting appropriate cultivars and optimizing planting schedules to enhance rice aroma and potentially improve yields by aligning planting with favourable conditions, contributing to higher market value and consumer satisfaction. Further research is needed to explore the specific environmental factors influencing aroma and to identify the genes responsible for desirable aroma traits to accelerate the development of superior aromatic rice varieties for the Konkan region. Further molecular analysis may help in understanding the genetic control of aroma under varying climatic conditions.

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