Evaluation of the parental and hybrid lines-Heterosis and other genetic parameters among Capsicum annuum genotypes and their hybrids

In most parts of the world pepper has become a popular spice that makes food hot in addition to its much needed nutrients of carotenoids and vitamins. This report has its objective to evaluate the parents and hybrid of three Nigerian pepper genotypes (Shombo, Tatase and Nsukka yellow pepper) for growth and yield; and to estimate their genetic parameters. Conventional breeding by hand pollination was adopted. The mean performance of the parents and hybrids for morpho-agronomic characters were evaluated. Heterosis and inbreeding depression were estimated. The F1 hybrids showed superiority over the parental genotypes with Sho x Nsky-rw having significantly (P ≤ 0.05) the highest value in most of the traits. In morphological traits, Sho x Nsky-rw hybrid had highest values in canopy diameter, number of leaves, number of nodes and number of branches per plant, while in fruit traits, it also had significantly the highest values in the number of fruits, fruit length and weight of fruits per plant. Sho x Nsky – rw had positive heterobeltiosis over the better parent in most of the yield and yield component characters. While Sho x Nsky – rw had the highest yield, Tat x Sho had the highest fruit wall thickness. The combinations of these traits are important to both the farmers and consumers. Having appropriate parents with genetic variability F1 pepper plants having distinct superiority above the mid and better parents could be developed.


INTRODUCTION
Pepper is a vegetable grown by small, medium and large producers or integrated to agro-business with a considerable socio-economic importance.Capsicum genus has been reported to be one of the important vegetables cultivated in Nigeria which is ranked in the third position after onion and tomato in the economic market (Maga, 2012).Diverse types of Capsicum species are cultivated widely in Africa where they are consumed as traditional vegetable or spice.Due to the great range of pepper products and by-products, uses and forms of consumption, it is an essential spice commodity and has formed an integral part of many diets in the world *Corresponding author.E-mail: ngozi.abu@unn.edu.ng.Tel: +234(0)8064664555.
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Table 1.Crossed in a complete diallelic mating system without reciprocal crosses to obtain F1 generation.
Capsicum species are usually self-compatible and selfpollinating crop (Raw, 2000;Onus and Pickersgill, 2004).Some percentage of outcrossing is associated with insect pollinators than with wind (Raw, 2000).Genetic advance (GA) under selection refers to the improvement of characters in genotypic value for the new population compared with the base population under one cycle of selection at given selection intensity (Singh, 2001).Therefore, genetic advance (GA) is important to predicting the expected genetic gain from one cycle of selection.Heterosis is one of the most important genetic tools for the manifestation of different cross combinations in crops and determining their potential for commercial exploitation under different environmental conditions (Ashfaq et al., 2013).This breeding method has been used extensively in agriculture to increase yield and to enlarge adaptability of hybrid varieties in a number of crop species (Meyer et al., 2004).The percentage increase or decrease in traits among the hybrids over the mid-parent and better parents' performance is used to assess the overall performance of these hybrids (Inamullah et al., 2006).Heterobeltiosis expresses the betterment over the better parent; likewise, standard heterosis expresses the heterosis over the standard varieties (Shrestha et al., 2011).The major goal of the research was to improve the red fruited pepper genotypes in relation to aroma and β-carotene; however, this report is aimed at evaluating the hybrid field performance as compared to the parents (Shombo, Tatase and Nsukka yellow pepper) and the estimation of heterosis

MATERIALS AND METHODS
The experiment was conducted at the Botanical Garden, University of Nigeria, Nsukka.The seed sources of the parental accessions were from a three year evaluation programme at the Faculty of Agriculture Farms, University of Nigeria, Nsukka.The F1 hybrids were generated between the highly aromatic genotype, Nsukka Yellow Pepper (Nsky -rw) and some red and fat fruited genotypes (Shombo and Tatase) with a view to improving the red fruited genotypes in relation to aroma from the Nsky -rw parent and improving the carotenoid content of the aromatic yellow pepper genotype (Nskyrw) from the red fruited genotypes (Shombo and Tatase).Hybridization was conventionally done by hand pollination (Morakinyo and Falusi, 1992) (Table 1).
Seeds from successful crosses were used to generate the F1 plants.The F1s were evaluated in the subsequent year and the seeds from F1 plants were used to raise the F2 plants.The parents, F1 and F2 plants were evaluated in the field using randomized complete design (RCBD).Cultural practices were maintained manually.The weeds were removed by manual weeding with small hoe.The data on plant height, mainstem length, mainstem internode length and canopy diameter were metrically measured in centimeters (cm).The parameter on the number of branches per plant, number of leaves per plant, number of nodes per branch, number of nodes per plant, number of nodes on main stem were collected by numerical count at one hundred to one hundred and five days after planting (DAP).The leaf area (cm 2 ) measurement was taken using the autoamated leaf area meter in the Physiology Laboratory of the Department of Crop Science, University of Nigeria, Nsukka.
The fruit attributes and yield were also studied and data were collected on fruit diameter (cm), fruit length (cm), fruit stalk length (cm) and Pericarp thickness (mm) -measured with Venier Caliper.The number of fruits per plant was by numerical count.Fresh fruit weight (g) per plant was also determined.The fruits were processed and the seeds were sun dried for five days in the Botanical garden; the average of the numerical count of seeds was recorded as number of seeds per fruit.Seed weight / fruit (g) was also determined.The yield in tonnes per hectare was estimated from fruit yield per plant using plant population per hectare.

Statistical and genetic analysis of data
Data collected on the quantitative characters were subjected to analysis of variance (using GenStat Discovery Edition 4 software) to test for significant differences among the treatments, while significant means were separated using Fisher's Least Significant Difference (F-LSD) at p < 0.05.
Estimation of Heterosis/ Hybrid vigor was achieved using the formula:

RESULTS AND DISCUSSION
The results of the field evaluation of the parents and hybrids are presented in Tables 2 and 3.There were significant variations across the traits among the parents and hybrids.The values for canopy diameter ranged from 37.9-66.92cm.Wider canopies could confer advantage in exposing the leaves to sunlight and more production of the fruit.Equally, high number of leaves together with high leaf area among the F 1 plants of Sho x Nskyrw is advantageous in attracting more sunlight energy thereby increasing assimilates from photosynthesis.Shombo had significantly the highest value in main stem length across the parent and other hybrid.Its hybrid (Sho x Nskyrw) equally significantly had the tallest plants with a mean value of 66.11 cm.This value did not, however, vary from Shombo parent and F 2 plants of Sho x Nskyrw.Tall plants could be disadvantageous in mechanical harvesting but could be preferred in positioning the leaves and tender branches for wider contact with sunlight.Sho x Nskyrw F 1 plants had significantly the shortest internodes (0.55 cm).These same F 1 plants (Sho x Nskyrw) also had significantly the highest number of nodes on the main stem, number of nodes/ branch, number of nodes/ plt and number of branches/ plt.This seems to suggest that the inheritance of shorter internodes could result in a significant increase in yield component characters that may have direct or indirect effect on fruit yield.These yield components have been shown to contribute to yield by having high correlations with fruit yield (Nandadevi and Hosamani, 2003).
The results of the fruit characters showed that Tatase had significantly the fattest fruits (2.03 cm diameter) while Shombo had significantly the longest fruits (7.76 cm) across the parents and hybrids (Table 3).Tatase parent which had the fattest fruits also had the longest fruit stalk length and the highest number of seeds/ fruits.This fat fruited genotype had the highest single fruit weight; however, it sets few fruits which is evidenced by the significantly low number of fruits per plant (14.83).Equally the F 1 hybrids (Tat x Nsky-rw) inherited this attribute of low number of fruits per plant (9.33).Tatase genotype has its preference in having high single fruit weight and thick pericarp as recorded in fruit wall thickness (3.54 cm) (Table 3).The highly aromatic genotype (Nsky-rw) had a relatively high yield (6.64 t/ha) which was significantly higher than the Tatase parent and the F 1 hybrids of Tat x Nsky-rw.The higher numbers of fruits recorded in Shombo parent and its F 1 hybrids (Sho x Nskyrw) were translated to higher cumulative yield of 11.1 and 11.28 t/ha, respectively.The red fruited genotype Shombo could be used as one of the parents in breeding programs due to its high yield.Shukri et al (2015) reported that genetic distance between parents used in breeding program is required in developing new parents with high performance in line with the breeders' objectives.It had earlier been reported that Shombo has a frutescens origin while Nsukka yellow pepper (Nskyrw) is purely Capsicum annuum (Morakinyo and Falusi, 1992).This tends to point out the genetic distance between these two parents, thus favouring the observed high performance.
Canopy diameter, number of leaves/ plt, number of nodes/ plt, leaf area and number of branches/ plt showed positive heterosis over the mid-parents in both hybrids, and all except number of leaves/ plt in Tat x Nsky-rw, showed positive heterobeltiosis over the better parent (Table 4).These traits are the major traits that contribute to yield in peppers.Nandadevi and Hosamani, (2003) reported a high correlation between these traits and pepper yield.It, therefore, implies that the increase in these yield component traits could significantly improve fruit yield among the F 1 plants.The F 1 hybrids of Tat x Nsky-rw had positive heterosis over the mid and betterparents (+42.69 and +34.84, respectively) in plant height.This peculiarity puts these F 1 plants at advantage in hand harvesting since taller plants are preferred.All the major yield component traits showed inbreeding depression in F 2 among Sho x Nskyrw plants.This is expected as there are allelic segregations at F 2 and pepper being predominantly self -pollinating would have high heterozygosity at F 1 .High heterozygosity favours heterosis in many plant species.The F 2 seeds of Tat x Nsky-rw failed in germination; this phenomenon had previously been observed in crosses by some researchers (Silva et al., 2017).
The estimation of heterosis over the mid and better parent and inbreeding depression in F 2 for fruit characters is presented in Table 5.The number of fruits/ plt is a major trait contributing to fruit yield in peppers and it has positive heterosis over both the mid and betterparent in Sho x Nskyrw (+113.65 and +103.42,respectively).It has been reported that number of fruits/ plt could predict yield with a high prediction accuracy (Abu et al., 2015).
Fruit weight together with fruit yield also had a positive heterosis over both the average and better parental values in Sho x Nskyrw.Superiority over the better parental values (heterobeltiosis) has been reported to be more effective than heterosis, particularly in the breeding of self-pollinating crops (Shukri et al., 2015).It should also be noted that most of the fruit characters had negative heterosis in Tat x Nskyrw.Tatase usually sets few fat fruits with high  internode length observed in Sho x Nskyrw hybrid was advantageous as it had the highest values in major morphological traits with high weightage to yield and in fruit yield.Equally, while Sho x Nskyrw had the highest yield, Tat x Sho had the highest fruit wall thickness.The combinations of these traits are important to both the farmers and consumers.The genetic distance between the Shombo and Nsukka yellow pepper was advantageous in raising F 1 hybrids with high performance above the better parent.
Mean of F1 = Mid parent value = Better parent value Differences between selfed (F2) and outcrossed (F1) progeny were Estimation of Heterosis/ Hybrid vigour was achieved using the formula below Heterosis over the mid parent Estimation of Heterosis/ Hybrid vigour was achieved using the formula below Heterosis over the mid parent parent value BP = Better parent value Gonza´lez et al. (2014) associated inbreeding depression with embryo mortality and a reduction in plant vigor.This could explain the germination failure of the F 1 seeds of Tat x Nsky-rw hybrids and the reduction in vigor among the F 2 hybrids of Sho x Nskyrw.In conclusion, the very short

Table 2 .
Mean performance of parents, F1 and F2 populations in morphological and yield component characters.

Table 3 .
Mean performance of parents, F1 and F2 populations in fruit characters.

Table 4 .
Estimation of heterosis over the mid and better parents and inbreeding depression for morphological traits.

Table 5 .
Estimation of heterosis over the mid and better parents and inbreeding depression for fruit characters.

x Nsky-rw Heterosis % Tat x Nsky-rw Inbreeding Depression Sho x Nsky-rw Inbreeding Depression Tat x Nsky- rw
2 plants of Sho x Nskyrw while in Tat x Nsky-rw, there were no survivals.