**5. Genetics of kernel elongation**

Kernel lengthwise increase without increase in girth is a desirable characteristic in high quality premium rice. Bao *et al.,* [18] reported that in *indica* rice variety, cooked kernel elongation was governed mainly by major gene with environmental interactions. Genetic improvement of any characters depends on efficiency of selection among the progenies which has different genetic value. Gene actions are reported to be associated with breeding value. To estimate the breeding value of progeny by studying the additive and dominance effects and their interactions which would benefit breeders to select the most appropriate breeding approaches to develop the superior variety.

Inheritance pattern of cooked kernel elongation ratio is controlled by single gene and influenced by some modifiers [13]. Kernel elongation governed by additive [19] or non-additive [20–28] or both additive and non additive gene action [29]. Hence genetics of kernel elongation has not been elucidated due to its complex nature and inconsistent pattern [30].

Elongation ratio and elongation index are highly heritable [31, 32]. This trait under polygenic control, involving epistasis, additivity, and genotype × environment interactions [33]. Three crosses were made among Mahsuri mutant, Mahsuri and 9192 to study the segregation pattern of cooked kernel elongation. The frequency distribution of kernel elongation ration of the population showed bimodal curve. However, in crosses of Mahsuri mutant and mahsuri (and its reciprocal crosses) the bimodal was skewed towards lower kernel elongation. Hence this character might be influenced by one or two loci [13].

The parental lines did not showed significant differences in kernel elongation ratio, however the progeny exhibited much larger range of variation due to transgressive segregation. It is difficult to conclude about inheritance pattern of kernel elongation in rice since the segregation pattern is not stable in different crosses and very little information is available on about inheritance pattern of kernel elongation of rice [34].

Genetic models used to analyse the cooked rice elongation traits of indica rice in two environments and identified that rice grain quality was mainly controlled by genotype, major gene effects and environment interactions. Milled and cooked rice length exhibited higher narrow sense heritability's than cooked rice elongation which indicate that early selection would be possible for milled and cooked rice length but not for cooked rice elongation [33].

### **6. Association of kernel elongation with other quality traits**

Waxy gene allele involved in determination of cooked rice elongation. The closely linked marker of waxy locus will facilitate the replacement of poor quality parent alleles [11] and waxy gene region control the cooked rice grain quality traits viz., elongation, length, width, width expansion ad water absorption [35]. Elongation index showed positive significant association with most of the grain quality traits which might be due to starch deformation caused by soaking or boiling.

Water absorption showed positive association with cooked rice elongation [36]. Aroma showed positive correlation with kernel elongation and both are highly influenced by environment. Elongation of rice can be influenced by both the l/b ratio and the amylose contents [37]. Kernel elongation is a physical phenomenon and influenced by gelatinization temperature [38]. Grain elongation has been associated with intermediate amylose and low gelatinization temperature.

Gene or quantitative trait loci for aroma and cooked kernel elongation were linked and present on chromosome 8.
