Development of Early Maturing Varieties in Groundnut (Arachis hypogaea L.)

Oilseed crops are an important determinant of agricultural economy, next to cereals within the segment of field crops. Groundnut (Arachis hypogaea L.) is the 3rd most important oil seed crop of the world cultivated in about 108 countries of world (Upadhyaya et al., 2003).
        
Among the major groundnut producing states of India, Gujarat stands first place in area and production of groundnut followed by Andhra Pradesh while yield per hectare (productivity) was high in Tamil Nadu followed by Rajasthan.
        
One of the solutions to increase yield and economic benefits is development of high yielding progenies with short crop duration or early-maturing trait. The highly indeterminate fruiting pattern of groundnut and the fact that the pods grow underground, make the prediction of groundnut maturity a difficult task with potentially large economicconsequences if an incorrect decision is made (Pattee et al., 1974). Considering all this itis experienced by the groundnut cultivators that the varieties with optimum maturingduration of nearly 100 days are profitable and also flexible in crop rotation.
        
As reported by Nigam (2014), while breeding for early maturity in groundnut, for the botanical characteristics and physiological behaviour of the crop, the following characteristics could be visualized: Short plant stature with shorter inter-nodal length, faster germination and emergence, fewer days to first flowering, and accumulation of a maximum number of early flowers and high shelling turnover. Such characters could be seen in the species Arachis hypogaea Subspecies fastigiata with botanical varieties fastigiata (Valencia type) and vulgaris (Spanish type) that have terminating flowering habits which is most suitable for the development of short duration progenies (Shokes and Melouk, 1995).
        
Upadhyaya and Nigam (1994) have reported that three independent genes with complete dominance governed the days to accumulation of 25 flowers while days to first flowering was governed by additive gene action of a single gene. In the cross between early and late maturing genotypes the segregation pattern of days to maturity was observed to be dominant-recessive epistasis. Hence, it provides a better opportunity to improve the complex trait of early maturity in groundnut through recombination breeding.
               
Thus, taking this research as a base, the present study was taken up to understand the complexity of maturity in groundnut and develop genetic stocks with a potential of early maturing and high yielding groundnut varieties.

In the present study, the established high yielding varieties with maturity duration more than 100 days VRI 8, CO 7, ICGV 07222 and VRI 6 were selected as female parents and early maturing source varieties VRI 3, Chico, ICGV 91114 and ICGV 93468 were selected as male parents. The parental variety details are furnished in the Table 1. Theses selected plants were crossed in l × t fashion.
 

        
The crosses were evaluated during kharif, 2019 and among the parental combinations the crosses VRI 8 x VRI 3 (C₁), CO 7 x Chico (C₂), ICGV 07222 x Chico (C₃), ICGV 07222 x ICGV 91114 (C₄) and VRI 6 x ICGV 93468 (C₅) with fair heterosis and promising mean performances for early maturity, pod and kernel yield per plant were further advanced to assess the nature of gene action by generation mean analysis by generating the backcross population to both the parents (B₁ and B₂) and F₂ population. The six generations of the selected crosses viz., P₁, P₂, F₁, F₂, B₁ and B₂ were sown in Randomized Block Design with two replications during rabi, 2020, at the Department of Oilseeds, Tamil Nadu Agricultural University. The number of plants studied per replication in each of the population in each cross is tabulated in the Table 2. The two main component characters to develop early maturity groundnut varieties are days to accumulation of 25 flowers and days to maturity were recorded for these plants.
 

        
The data for the six generations of the selected crosses viz., P₁, P₂, F₁, F₂, B₁ and B₂ were subjected to six parameter model of generation mean analysis using Mather and Jinks (1982) method followed by association analysis for the early maturing traits towards yield using the method suggested by Johnson et al., (1955).
               
The resultant genetic stocks selected for the objectives were also scored for late leaf spot and rust using validated SSR markers (GM1573, GM1009, seq 8D09, GM2009, GM1536 and IPAHM103) to suggest valid breeding programmes for further improvement.

For both the traits under study the joint scale test, exhibited significance for either of the two scales A and B of C and D in all the crosses indicating the presence of non-allelic interactions. Further, the gene action for the two traits is furnished hereunder.
 
Days to accumulation of 25 flowers
 
The second backcross generations (B₂) of the crosses   CO 7 × Chico recorded the lowest days to accumulation of 25 flowers in comparison to all the generations of the other crosses except to that of the male parents. The F₁s of the crosses CO 7 × Chico and ICGV 07222 × Chico recorded significant lower days for DTF (Table 3).
 

       
All the crosses recorded significant positive dominant (h) gene action for the trait days to accumulation of 25 flowers. In addition to this all the crosses recorded various other interactions that are described hereunder.
       
The crosses VRI 8 × VRI 3, CO 7 × Chico, ICGV 07222 × ICGV 91114 and VRI 6 × ICGV 93468 recorded dominant (h) and dominant × dominant (l) effects in opposite direction suggesting duplicate epistasis. The crosses ICGV 07222 × Chico, ICGV 07222 × ICGV 91114 and VRI 6 × ICGV 93468 recorded significant additive × additive (i) interaction (Table 4 and 5). Thus, the trait displays duplicate dominant epistasis with additive effect resulting in reduced heterosis and selection for the trait would surely lead to fruitful genetic gain. These results are in confirmation with that reported by Gadakh et al., (2019) for days to 50% flowering in groundnut. They have recorded dominant epistasis with additive, additive × additive and dominant × dominant effects. Also Upadhyaya and Nigam (1994) have reported duplicate dominant effects for days to accumulation of 25 flowers in groundnut. In genetic analysis of yield contributing traits in groundnut Alam et al., (2013) have reported additive gene effects for days to 50% flowering. On awhole the trait days to accumulation of 25 flowers exhibits significant dominant effectsand duplicate epistasis suggesting that pedigree breeding would enable improvement.
 

 

 
Days to maturity
 
In the present study the parents are deliberately selected to generate segregating material with lower maturity duration in groundnut. The F₁s of all the crosses displayed intermediate values for days to maturity lower than the female parent show casing negative heterosis (Table 6).
 

       
The crosses recorded significant for additive (d), dominance (h), additive × additive (i), additive × dominant (j) and dominant × dominant gene interactions with h and l in opposite direction (Table 7 and 8). The result reveals the presence of duplicate epistasis. Similar results were reported by Halward and Wynne (1991) for days to maturity in groundnut.
 

 

       
In all the crosses the additive × dominant (j) effect was negatively significant while the magnitude of dominance (h) and additive × additive (i) were higher than that of additive (d). Thus, in all the crosses the presence of duplicate epistasis and significant additive, dominance and non-allelic interactions indicates that it is worthwhile to intermate the selected ones in segregating generations, which could result in the accumulation of favourable genes. Hence, biparental mating or few cycles of recurrent selection followed by pedigree method of selection may be followed for bringing improvement in this trait.
       
The B₁ generation of the cross ICGV 07222 × Chico (109.06 days) recorded 7.48% reduction in maturity duration than ICGV 07222 and high pod and kernel yield over CO 7. In the cross VRI 6 × ICGV 93468 the B₁ (109.08 days) generation was early by 4.85% than VRI 6 and higher in pod yield than CO 7. The progeny B₁ of ICGV 07222 × ICGV 91114 recorded higher pod, kernel and oil yield than CO 7 with a mean maturity duration of 109.24 days. This was a reduction of about 7.85% in maturity duration than that of ICGV 07222.
       
All these progenies exhibited moderate to resistant reaction to foliar diseases. Hence, forwarding of the genotypes could be done through pedigree breeding with simple selection. Scoring of these progenies for late leaf spot and rust resulted as the derivatives F₂ and B₂ of CO7 × Chico are susceptible to foliar diseases which could be subjected to pedigree and resistant breeding for advancement. The progenies B₁ of ICGV 07222 × Chico, VRI 6 × ICGV 93468 and ICGV 07222 × ICGV 91114 could be forwarded through selection. A quick comparison of the selected genotypes to standard check CO 7 is provided in the Table 9.
 

       
The trait pod yield per plant exhibited positively significant correlation with days to accumulation of 25 flowers, days to maturity in all the crosses (Table 10). Thus, increase in these traits would result in increase of pod yield and are useful as selection criteria for the improvement of yield. It is evident from this study that the trait days to accumulation of 25 flowers is positively correlated to days to maturity which is also supported by the research works of Seshadri (1962) and Yadava et al., (1984). Hence, the trait - days to accumulation of 25 flowers is the major selection factor for early maturity in groundnut.
 

               
The study conducted with the aim of developing early maturing and high yielding progenies of groundnut with high oil content, a crossing program was steered involving genotypes of diverse origin. The developed derivatives from the study are F₂ and B₂ of CO 7 × Chico, B₁of ICGV 07222 × Chico, ICGV 07222 × ICGV 91114 and VRI 6 × ICGV 93468 could be forwarded for further development of successful early maturing groundnut varieties. The study resulted in the assembly of genetic stocks having potential to develop successful groundnut varieties beneficial to the groundnut cultivating farmers of India.