Breeding for Dwarfism and Aroma Enhancement in Basmati 370 Rice

Abstract

Basmati 370 rice (BS370) is popularly grown in many parts of the world for its good aroma and long, slender grains with excellent cooking and eating qualities. However, Basmati’s tall stature and weak stem structure render it susceptible to lodging. This happens particularly when Basmati is subjected to high doses of nitrogenous fertilizer which leads to grain loss. Lodging reduces the efficiency of mechanized harvesting, which is commonly used for large-scale rice production, and further aggravates pre-harvest losses. A transformation of BS370 to a short-statured plant is crucial to address this challenge. This study's primary research objective was to create a semi-dwarf rice line of BS370 origin while retaining the Basmati-like aromatic quality. To realize this objective, Basmati 370, being the female parent, was crossed with a semi-dwarf variety, IR64 using the manual hybridization technique. For confirmation of successful hybrids, distinct anthocyanin pigmentation was used. Thereafter, pyramiding of aroma genes was performed where BS217 was crossed with BS370 to retain the aroma trait in BS370. This was followed by using unique anthocyanin pigmentation selection and molecular marker-assisted selection to distinguish successful from non-successful crosses. Molecular marker-assisted selection was performed to confirm whether the distinctive aroma gene in Basmati rice was retained. The F1s from the cross between BS370/IR64 and BS217/BS370 were then crossed and the resulting semi-dwarf aromatic lines underwent backcrossing with Basmati 370 as the recurrent parent and selfing up to BC1F2. The BC1F2 populations and parents were evaluated for agronomic performance at KALRO, Mwea in a randomized complete block design replicated thrice. Data on agro-morphologic traits was collected and subjected to analysis of variance (ANOVA) on SAS 9.4 software. Tukey's HSD test at P≤0.05 was employed to compare the means of different traits among the genotypes. The findings from this study demonstrated the successful development of an aromatic, semi-dwarf BS370 rice line. The improved line exhibited significantly reduced plant height, shortened culm length, and moderately shorter leaf length. Specifically, plant height was reduced by an average of 34 cm, culm length by 7 cm, and leaf length by 27 cm, compared to the tall parent, BS370. The study was also able to select homozygous fragrant semi-dwarf plants confirming the successful retention of both the fragrance and semi-dwarfing gene in Basmati 370. This breakthrough offers promising prospects for increased food security through reduced grain loss, and improved efficiency in mechanized harvesting. The successful incorporation of the sd-1 gene and aroma into Basmati 370 resulted in a significantly decreased plant height and aromatic breeding line. This breeding line can be further selected for better performance and released as a new cultivar. Once stabilized in advanced filial generations, the new semi-dwarf aromatic line will positively impact rice yield since the dwarf stature will reduce the plant lodging. This will ultimately benefit Kenyan Basmati rice farmers and satisfy consumers' preferences, which will expand the rice industry as a whole.