Heterotic Studies For Yield and Yield Components Coupled with Stem Rot Resistance in Groundnut (Arachis hypogaea L.)

Introduction:

Groundnut is well known important oilseed crop in the world and in India because of its economic importance. The seed is comprised of 40-54 per cent oil, 25-28 per cent protein and 18 per cent of carbohydrates in addition to minerals and vitamins including vitamin E, niacin, phosphorus, falcin, calcium, riboflavin, magnesium, zinc, iron, thiamine, and potassium.

Glоbаlly, it is сultivаted in аn аreа оf 29.92 Mhа with аnnuаl рrоduсtiоn оf 55.30 Mt and productivity of 1851 kg hа^-1 [1]. In Indiа, grоundnut соvers аn аreа оf 60.9 lаkh hа with а рrоduсtiоn оf 10.21 Mt аnd рrоduсtivity оf 1676 kg hа^-1. In Аndhrа Рrаdesh, it is сultivаted in аn аreа оf 8.24 lаkh hа with а рrоduсtiоn оf 5.19 Mt аnd рrоduсtivity оf 631 kg hа^-1 [2]. Among the major groundnut-growing states of India, Gujarat and Andhra Pradesh are ranking first and second in terms of area, respectively.

 The major growing states are Gujarat, Andhra Pradesh, Telangana, Tamil Nadu, Karnataka, Rajasthan and Maharashtra. These constitute around 80 per cent of total area and production. In Andhra Pradesh, Several factors like edaphic, climate, pests and diseases prevailing in the environment hinders yield, especially stem rot disease incidence at the time of harvest causing yield loss up to 25 %. Hence, there is a need to focus on the enhancement of yield along with stem rot resistance through breeding followed by meticulous selection in advanced generations.

The superiority of F₁ over the parents in terms of yield or some other yield-related traits is commonly referred to as heterosis or hybrid vigor. The commercial exploitation of heterosis in groundnut has limited application because of the practical difficulties of the cleistogamous nature of flower, difficulty in emasculation, pollination of flowers and hybrid seed production in sufficient quantity. However, the nature and magnitude of heterosis help in identifying superior cross combinations and their exploitation to get better transgressive segregants in the advanced generations [3]. Exploitation of heterosis is of direct interest for developing hybrids in cross-pollinated crops but it is also of importance in self-pollinated crops where such feasibility existed. The allopolyploidy nature of groundnut will also favor the preservation of such hybrid vigor for a considerable number of generations. The knowledge of heterosis would also help in the elimination of poor crosses in the early generation of testing itself.

Hence, the heterosis assumes importance in breeding as heterotic crosses have the potential to throw out superior segregants in subsequent generations. The estimates of heterosis provide information about the nature of gene action involved in the expression of yield and its contributing traits. The information is also essential to formulate efficient breeding program for the improvement of the crop. In the present investigation, the standard heterosis was calculated with the ‘Kadiri-6’ variety as the check variety in the control condition as it was the most popular and preferred national check variety in recent years and ‘J-11’ variety in the sick plot condition as it was a most popular tolerant check for stem rot incidence. For the traits viz., days to 50% flowering, days to maturity, SLA at 60 DAS, plant height and number of immature pods plant^-1 the heterosis in the negative direction is generally considered desirable.

2. Material and Methods:

The experimental material for this study consisted of nine parents (five lines viz., Kadiri-6, Narayani, TAG-24, ICGV-07262 and ICGV-91114 and four testers viz., TCGS-1862, TCGS-2149, J-11, and CS-19) and 20 F₁ crosses derived by line x tester mating fashion among the parents (kharif, 2019). The salient features of parents are presented in Table 1.

The nine parents and 20 F₁ crosses were sown in randomized block design, replicated twice during rabi, 2019 in sick plot (Plate 1) and control condition (Plate 2) simultaneously. Each entry was sown in a row by dibbling the seeds in 3 m length, with a spacing of 30 cm between the rows and 10 cm within the row. The crop was artificially inoculated with sclerotium fungus multiplied in sorghum grains between inter rows followed by mulching with paddy straw to the entire field after 30 DAS, 60 DAS and irrigation was given frequently through drip pipes to conserve moisture which aggravate the mycelium and aids in further multiplication in the sick plot. Common crop management practices like plant protection, weeding and irrigation were carried out to maintain good crop growth in controlled conditions. Each entry was grown in two rows of 3 m in length with a spacing of 22.5 x 10 cm. Data was recorded in 5 randomly selected plants for yield and yield components along with PDI (Percent Disease Incidence) at maturity recorded as per the procedure outlined by [4]. The observations were recorded on five randomly tagged competitive plants from the centre of row in each genotype in each replication for all the yield and yield component traits (SCMR at 60 DAS, SLA at 60 DAS, harvest index, plant height, number of primary branches per plant, number of pegs per plant, number of pods per plant, number of mature pods per plant, number of immature pods per plant, 100 pod weight, 100 kernel weight, sound mature kernel %, shelling percent, dry haulm yield per plant, pod yield per plant, kernel yield per plant, oil and protein content) except days to 50% flowering and days to maturity which were recorded on per plot basis. The mean of these five plants were used to compute mid-parent heterosis (MH), better-parent heterosis (BH) and standard-heterosis (SH). Percent mid-parent heterosis (MH), better-parent heterosis (BH) and standard- heterosis for twenty traits were presented from Tables 2 to 13 respectively. The superiority of F₁ over the mid-parent and better-parent was estimated as per the formula given by [5] and [6] respectively. The significance of heterosis was tested by using ‘t-test’ as suggested by [7] and [8].

3. Results and Discussion:

The degree of heterosis varied from cross to cross for all the traits. Considerable heterosis in certain crosses and low heterosis in others revealed varied nature of genetic diversity and gene action with the genetic make-up of the parents used in the present study. Percent mid-parent heterosis (MH), better-parent heterosis (BH) and standard-heterosis (SH) for yield, yield components and stem rot resistance in sick plot condition and control condition among 20 F₁ crosses of groundnut was furnished in Table 2 to 13.

3.1 Mid-parent heterosis:

Mid-parent heterosis is useful in the identification of crosses showing the presence of a dominant gene effect. In sick plot condition, two crosses viz., ICGV-91114 x TCGS-1862  (-8.06%) and ICGV-91114 x TCGS-2149(-8.47%) recorded desirable mid-parent heterosis for early flowering. Similarly, three crosses viz., TAG-24 x TCGS-2149 (-5.78), Kadir-6 x J-11(-4.72), and ICGV-07262 x TCGS-2149 (-4.60) have registered mid-parent heterosis in desirable direction for early maturity. In the contrary, two crosses viz., TAG-24 x TCGS-1862 (-5.70%) and ICGV-91114 x CS-19 (-8.73%) registered desirable negative and significant mid-parent heterosis for days to maturity. Hence, these crosses could yield early flowering segregants in further generations. Desirable negative and significant heterosis in earliness helps the crop to escape from late-stage abiotic stress i.e., drought conditions. [9], [10], [11], [12], [13] and [14] also revealed negative mid-parent heterosis for early flowering and maturity in their studies.

Interestingly, all F₁ crosses in sick plot and control condition registered mid-parent heterosis for SLA at 60 DAS except TAG-24 x TCGS-1862, ICGV-91114 x TCGS-2149 and ICGV-91114 x J-11 in sick plot condition suggesting that these crosses could be exploited for the development of desirable water use efficient groundnut genotypes as they recorded negative and significant mid parent heterosis for this character.  In groundnut low SLA is desirable because it has been demonstrated that variation in water use efficiency was caused by variation in photosynthetic capacity [15] and a significant negative correlation between photosynthetic capacity and SLA [16].

Among the crosses, Narayani x J11 exhibited mid-parent heterosis for the traits viz., number of flowers plant^-1from 25 to 50 DAS (sick:24.17%; control:22.44%), number of pegs plant^-1(sick:41.93%;control:26.76%), number of pods plant^-1(sick:26.22%; control:42.56%), number of mature pods plant^-1  (sick:17.94%; control:48.54%), Sound Mature kernel (%) (sick:7.87% ; control:3.82%), dry haulm weight plant^-1(sick:88.82%;control:46.14%), pod yield plant^-1(sick:33.98%;control:8.52%), kernel yield plant^-1(sick:56.10% ;control:13.40%) and PDI at maturity (sick:-55.77%; control:-99.82%) in a desirable direction.

Similarly, Kadiri-6 x CS-19 reported significant heterosis over mid-parent in desirable direction for the traits viz., number of pods plant^-1(sick: 13.11%; control:16.25%), number of immature pods plant^-1(sick:-55.96%;control:-30.49%), number of mature pods plant^-1 (sick:22.54%; control:25.88%), dry haulm weight plant^-1(sick:67.94%; control:46.02%), pod yield plant^-1 (sick:30.67%; control:9.24%), kernel yield plant^-1 (sick:38.25%; control:14.39%) and PDI at maturity (sick:-73.85% ; control:-99.73%). 

Another cross ICGV-07262 x TCGS-2149 recorded desirable significant mid-parent heterosis for the traits viz., number of flowers plant^-1from 25 to 50 DAS (sick:10.11%;control:8.12%), SMK(%) (sick: 13.68%;control:4.57%), dry haulm weight plant^-1 (sick:87.90%; control:53.86%), pod yield plant^-1 (sick:28.38%; control:7.32%), kernel yield plant^-1(sick:71.12%;control:12.37%) and PDI at maturity (sick:-48.48%;control:0.00%).

The next better choice is ICGV-07262 x TCGS-1862 showed positive and significant mid-parent heterosis for the traits viz., SCMR at 60 DAS (sick:9.83%; control:7.97%), number of pods plant^-1, (sick:26.83%;control:17.62%), dry haulm weight plant^-1 (sick:94.71%; control:65.47%), pod yield plant^-1 (sick:28.11%; control:19.00%), kernel yield plant^-1(sick:65.76%;control:26.84%) and PDI at maturity (sick:-56.00%; control:0.00%). The cross, TAG-24 x TCGS-2149 (9.15%) is identified as best heterotic cross for harvest index in control condition.

The present study affirmed the manifestation of heterosis in yield through heterosis of its component traits. The result of mid-parent heterosis in desirable direction for SCMR at 60 DAS, number of podsplant^-1, dry haulm weightplant^-1, pod yield and kernel yield plant^-1was in congruence with the reports of [12]. [17] reported the desirable mid-parent heterosis for a number of pods plant^-1, sound mature kernel %, pod yield and kernel yieldplant^-1 in their study. Similar kind of desirable mid-heterosis for a number of pods plant^-1, a number of mature pods plant^-1, pod yield and kernel yield plant^-1 was in agreement with the findings of [13].

3.2. Better-parent heterosis:

The appreciable magnitude of heterosis for important yield and yield components over better parent was perceived in the present study. This type of heterosis is evident to identify the presence of over-dominant effects for specific traits. The crosses viz., ICGV-91114 x TCGS-1862 (-17.39%), ICGV-91114 x TCGS-2149 (-14.29%), ICGV-91114 x J-11 (-12.50%), ICGV-91114 x CS-19 (-12.12%) flowered earlier than better parent while the crosses viz., ICGV-91114 x TCGS-2149 (-11.16%), ICGV-91114 x TCGS-1862 (-9.55%), ICGV-91114 x J-11 (-8.52%), ICGV-07262 x TCGS-2149, ICGV-07262 x CS-19 (-6.44%) and TAG-24 x TCGS-2149 attained early maturity than the better parent in sick plot. The crosses viz., Kadiri-6 x TCGS-2149 (-16.67%), TAG 24 x TCGS-2149 (-15.15%) and TAG 24 x J-11, TAG 24 x CS-19, Kadiri-6 x TCGS-1862 (-12.12%) attained early flowering in control condition. Likewise, the crosses viz., Narayani x TCGS-1862 (-10.92%), Narayani x J-11 (-10.57%), TAG-24 x TCGS-1862 (-9.66%), ICGV-91114 x CS-19 (-9.57%), Kadiri-6 x TCGS-1862 (-6.72%), Narayani x CS-19(-6.52%), ICGV-07262 x TCGS-1862(-6.30%), Narayani x TCGS-2149 (-6.19%) also registered desirable better-parent heterosis in control condition. Since line, ICGV-91114 and tester TCGS-2149 are common parents in most of the crosses and thus they were identified as the better parents for earliness in the present study. Similar results conformed with the findings of [12] and [14] for earliness traits.

The next best heterotic cross identified in the present study was Kadir-6 x CS-19 as it recorded higher magnitude of heterosis for number of pods plant^-1 (sick:12.02%; control:8.77%), number of immature pods plant^-1 (sick:-58.08%; control:-32.94%), number of mature pods plant^-1 (sick:22.03%; control:15.44%), dry haulm weight plant^-1 (sick:53.49% ;control:39.89%), pod yield plant^-1 (sick:30.05%; control:9.08%), kernel yield plant^-1 (sick:26.48%; control:10.43%) percent disease incidence at maturity (sick:-85.14% ;control:-99.86%) and protein content (%) (control:7.03%).

The F₁ cross ICGV-07262 x TCGS-1862 recorded desirable heterosis for SCMR at 60 DAS (Sick: 9.57%; control:3.98%), number of pods plant^-1 (sick:9.05%; control:10.82%), dry haulm weight plant^-1 (sick:24.12%; control:8.36%), pod yield plant^-1 (sick:56.06%; control:12.66%), percent disease incidence at maturity (sick:-73.45%; control:0.00%) and number of primary branches plant^-1 (Sick: 32.65%.). Another heterotic cross ICGV-07262 x TCGS-2149 displayed desirable better-parent heterosis for number of flowers plant^-1 (sick:6.99%; control:6.30%), sound mature kernel % (sick:7.35%; control:4.10%), dry haulm weight plant^-1 (sick:73.63%; control:50.25%), pod yield plant^-1 (sick:17.07%; control:2.36%), kernel yield plant^-1 (sick:57.75%; control:10.29%), percent disease incidence at maturity (sick:-70.69%; control:0.00 %), number of primary branches plant^-1 (sick:75%), number of flowers per plant^-1 (Sick:6.99%) and shelling per cent (sick: 31.51%).Similarly, the crosses viz., ICGV-07262 x J-11 and Kadiri-6 x J-11 were reported as a best heterotic cross for hundred pod weight (sick: 27.51%) and number of secondary branches plant^-1 (sick: 45.45%), respectively. Additionally, the crosses viz., Kadiri-6 x J-11(45.45%) and Kadiri-6 x CS-19 (28.12%) for a number of secondary branches plant^-1 and Narayani x TCGS-1862 (15.74%) revealed better parent heterosis in sick plot condition.

Six crosses viz., ICGV-07262 x CS-19 (12.05%), ICGV-91114 x TCGS-1862 (9.50%), TAG-24 x TCGS-2149 (9.15%), TAG-24 x CS-19 (7.11%), Narayani x CS-19 (6.26%) and Kadiri-6 x TCGS-1862 (5.77%) in control condition noticed the better parent heterosis for harvest index suggesting that these crosses could be utilized for development of high yielding groundnut varieties through intermating followed by meticulous selection in later generation. Likewise, two crosses viz., ICGV-91114 x TCGS-1862 (-26.67%) and ICGV-91114 x TCGS-2149 (-24.87%) registered desirable negative heterosis for plant height in the control condition.

A similar kind of positive and significantly better-parent heterosis was also reported in the studies of [11] and [18] for sound mature kernel %, [12] for a number of pods plant^-1, dry haulm weight plant^-1, pod yield and kernel yield plant^-1 and [13] for number of mature pods plant^-1. The results were in conformity with the findings of [14] for the number of pegs, number of podsplant^-1, pod yield and kernel yield plant^-1. From the current and previous studies, it is evident that better parent heterosis for yield and yield attributes are the resultant of over-dominant effects.

• Standard-heterosis:

Standard-heterosis is of direct practical value in plant breeding in the identification of superior genotypes for commercial release. The cross Narayani x J-11 registered positive and significant standard-heterosis for number of flowers plant^-1 (sick:43.53%; control:42.61%), number of pegs plant^-1 (sick:27.94%; control:58.73%), number of pods plant^-1 (sick:12.26%; control:18.52%), number of mature pods plant^-1 (sick:10.16%; control:29.03%), sound mature kernel % (sick:4.45%;  control:5.43%), dry haulm weight plant^-1 (sick:49.30%;control:50.04%), pod yield plant^-1 (sick:29.44%; control:14.91%), kernel yield plant^-1 (sick:67.07%; control:10.60%), percent disease incidence at maturity (sick:-78.00%;control:-100.00%), 100 pod weight (control:11.41%), 100 kernel weight (sick:7.91%) and shelling  per cent (22.76%).

The cross Kadir-6 x CS-19 recorded higher magnitude of heterosis for number of pods plant^-1 (sick:12.02%; control:8.77%), number of immature pods plant^-1 (sick:-58.08%; control:-27.85%), number of mature pods plant^-1(sick:22.03%; control:15.44%), dry haulm weight plant^-1 (sick:53.49%;control:52.72%), pod yield plant^-1 (sick:30.05%; control:9.40%), kernel yield plant^-1 (sick:52.44%; control:18.64%), percent disease incidence at maturity (sick:-85.14% ;control:-100.00%), 100 pod weight (control: 11.94%) and shelling per cent (sick:17.60%).

The cross ICGV-07262 x TCGS-1862 displayed desirable heterosis for SCMR at 60 DAS (Sick: 3.58% ; control:13.37% ), number of pods plant^-1 (sick:18.75%; control:13.84%), dry haulm weight plant^-1 (sick:71.16%;control:74.53%), pod yield plant^-1 (sick:39.17%; control:19.54%), percent disease incidence at maturity (sick:-78.00% ;control:-100.00%), number of primary branches plant^-1 (sick:44.44%), number of pegs plant^-1 (control:53.97%) and 100 pod weight (control:9.08%).

Another heterotic cross ICGV-07262 x TCGS-2149 registered desirable standard heterosis for number of flowers plant^-1 (sick:44.12%; control:43.75%), sound mature kernel % (sick:5.63%;control:6.30%), dry haulm weight plant^-1 (sick:64.74%;control:62.42%), pod yield plant^-1 (sick:31.27%; control:12.92%), kernel yield plant^-1 (sick:65.45%; control:20.08%), percent disease incidence at maturity (sick:-75.71% ;control:-100.00 %), number of primary branches plant^-1 (sick:40.00%), number of pegsplant^-1 (control:59.26%), 100 pod weight (control:10.06%) and shelling per cent (sick:25.99%).

Four crosses in sick plot condition and nine crosses in the control condition were found as best heterotic crosses for harvest index. Desirable negative heterosis of   -14.32% for plant height was recorded in the cross TAG-24 x TCGS-1862 in sick plot condition where as seven crosses viz., Kadir-6 x TCGS-1862 (122.22%),Kadir-6 x TCGS-2149 (94.44%), Kadir-6 x J-11 (122.22%),Kadir-6 x CS-19 (222.22%), Narayani x TCGS-1862 (166.67%), Narayani x TCGS-2149 (127.78%) and Narayani x TCGS-CS-19 (105.56%) over Kadiri-6 revealed desirable heterosis for number of secondary branches plant^-1 in control condition.

Further, it was also observed that all the crosses registered desirable standard heterosis for a number of flowers plant^-1 in both the conditions, hence these crosses could be exploited to develop reproductive efficient groundnut genotypes through rigorous selection in later generations. Four crosses viz., Narayani x J-11, Kadiri-6 x CS-19, ICGV-07262 x TCGS-1862, and ICGV-07262 x TCGS-2149 were identified as superior heterotic crosses in order to isolate genotypes with high water use efficiency in view of their positive standard heterosis for SCMR at 60 DAS and negative standard heterosis for SLA at 60 DAS in control condition.

A similar kind of desirable standard heterosis was also documented by [17] for a number of pods plant^-1 and pod yield plant^-1 and [13] reported the positive and significant standard heterosis for a number of mature pods plant^-1, pod yield plant^-1 and kernel yield plant^-1. 

From the above results it is to conclude that four crosses viz., Narayani x J-11, Kadiri-6 x CS-19, ICGV-07262 x TCGS-1862, and ICGV-07262 x TCGS-2149 in both the conditions were found to be the reservoir for the majority of yield and yield attributing traits which displayed desirable heterosis were governed by dominant alleles and heterosis in F₁s was a result of dominant and over-dominant gene effects. Hence these traits are advanced for direct selection to enhance vigor gain.

The high magnitude of heterosis was observed for most of the traits in all the crosses indicating the role of non-additive gene action in their expression. Based on the results of mean performance, combining ability and heterosis in sick plot and control condition the crosses viz., Kadiri-6 x CS-19, Narayani x J-11, ICGV-07262 x TCGS-1862 and ICGV-07262 x TCGS-2149 were considered as worthy combinations for enhancing pod yield coupled with stem rot resistance in groundnut.

With respect to combining ability effects and heterosis, the following broad inferences could be drawn from the present study i.e.,the crosses exhibiting high heterosis with desirable SCA effects did not always involve parents with high GCA effects, thereby suggesting the importance of interallelic interactions. However, it was also observed that at least one good general combiner was involved in best-performing cross combinations.

Thus, the potentiality of a genotype to be used as a parent in hybridization, or a cross to be used for recombination breeding may be judged by comparing perse performance of parents and crosses, along with combining ability effects of parents and heterotic response of crosses.

4. Conclusion:

The cross, ICGV-07262 x TCGS-1862 was identified as the best heterotic cross for pod yield plant^-1 and its components and the predominance of over-dominance effects was observed for yield and its components over standard resistant tester J-11 to the extent of 39.17% in sick plot condition and over standard line Kadiri-6 to the extent of 19.54% in control condition, respectively. The crosses viz., Narayani x J-11, Kadiri-6 x CS-19, ICGV-07262 x TCGS-1862, and ICGV-07262 x TCGS-2149 were identified as best cross combinations for both yield and stem rot resistance.

ACKNOWLEDGEMENT:

K. Amarnath is thankful to the NFST fellowship (National Fellowship for Scheduled Tribes, Government of India) for aiding financial assistance during the course of study and S.V. Agricultural College, Tirupati, ANGRAU for providing resources for carrying out doctoral research work.

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