Abstract: Background and Objective: Exploitation of heterosis is one of the practical means of increasing yield and information on the magnitude of heterosis is a basic requisite for identifying crosses that exhibit high amount of exploitable heterosis in hot pepper. The heterosis study was conducted with the objectives of determining the magnitude of heterosis and heterobeltiosis for yield and quality and to identify and select superior F1 hybrids for yield and quality improvement in hot pepper genotypes. Materials and Methods: The field experiment was conducted during 2014 through 2016 at six environments in Southern Ethiopia using 55 hot pepper genotypes that included 10 hot pepper parents and 45 F1 hybrids obtained from 10×10 half diallel crosses. It was laid out using RCBD with 3 replications and data collected was analyzed using Microsoft excel version 2013. Results: Analysis of mid and better parent heterosis confirmed that heterosis ranged from -51.50% in fruit dry weight to 97.66% in fresh fruit yield indicating the existence of sufficient heterosis that can be exploited in hot pepper breeding programs. Fresh fruit yield had mid and better parent heterosis ranging from -38.63 to 97.66% and from -47.24 to 80.44%, respectively. The highest heterosis for oleoresin content were recorded for Melkazala×Avpp59328, Avpp8913×Avpp0512, Marakofana×Avpp0206, Avpp0206×Avpp0105 and Melkazala×Avpp0514. The best selected hybrids in percentage mid and better parent heterosis for fresh fruit and dry weight yield include Melkashote×Avpp59328, Marakofana×Avpp59328, Melkashote×Avpp0105, Avpp0514×Avpp0105 and Avpp9813×Avpp0514. Conclusion: The investigation confirmed the existence of variable genetic potential for exploitation of heterosis for yield and quality including oleoresin content in Capsicum.
INTRODUCTION
Hot pepper (Capsicum annuum L.), (2n = 24), in the family Solonaceae, is an important spice and vegetable crop1,2. Pepper has diverse uses as spice, condiment, culinary supplement, medicine, vegetable and ornamental plant and is an indispensable spice due to its pungency, taste, appealing color and flavor. It is the second largest commodity after black pepper (Piper nigrum) in the international spice trade3,4.
Hot pepper is one of the major vegetable crops which covers 67.98% of the area in which vegetables are produced in Ethiopia5. The country has been producing paprika and Capsicum oleoresins for the export market. Hot pepper is an important traditional crop mainly valued for its pungency and color, hence, it has wide use in Ethiopian diet. The crop serves as the source of income particularly for smallholder producers and also contributes significantly to house hold food security in many parts of rural Ethiopia3-7.
Heterosis is the expression of superiority of F1 hybrid over the parents in a given trait8,9, assessed not by absolute value of a trait, but by its usefulness for practical advantages10. In another words, heterosis can be explained as increasing of the character value of F1 hybrids compared to the average value of both parents11,12. Heterosis in a desirable direction (hybrid vigor) is the ultimate aim of a plant breeder. In most cases, two major types of estimation of heterosis are reported in literature: (1) Namely mid parent or average heterosis, with superiority of the F1 over the mean of the two parents and (2) Better parent heterosis (heterobeltiosis), which is the increased vigor of the F1 over the better parent13-15.
Heterosis has been widely used in agriculture to increase yield and to broaden adaptability of hybrid varieties in a number of crop species8. Exploitation of heterosis was indicated as practical means of increasing yield and other economic traits in Capsicum peppers16. Information on the magnitude of heterosis in different cross combinations is a basic requisite to for identifying crosses that exhibit high amounts of exploitable heterosis11.
Extensive work on various aspects of heterosis in vegetable crops has been carried out and tremendous improvement has been made in its exploitation over the past several years17. There are many earlier reports indicating the exploitation of heterosis in the development of hybrid varieties in Capsicum species.
Some authors agree that Ethiopia is the center of origin for some Capsicum species which have immense genetic diversity in the country17. Yet production and productivity are challenged by many factors among which improved variety limitation hybrid production for traits of interest are among the core ones. Although such genetic studies have been made in various crops, including pepper, in various parts of the world, little or no effort has been made on pepper under Ethiopian conditions to exploit the existing potential. In this study, therefore, an attempt was made to generate information on six introduced and four released cultivars of pepper crossed in half-diallel fashion with the following objectives:
| • | To determine the magnitude of heterosis and heterobeltiosis for fresh pod yield and quality traits |
| • | To identify and select superior F1 hybrids for yield and quality improvement |
MATERIALS AND METHODS
Description of the study areas: The field experiment was performed in six different environments from 2014 through 2016 cropping seasons. The first crossing work was done at 2 locations Wolaita Sodo and Areka (Dubo) to obtain F1 crosses. Evaluation of F1 crosses with the parental materials was conducted at 3 different locations (Wolaita Soddo, Alaba and Humbo) that represent major pepper growing areas in Southern Ethiopia for two cropping seasons that gave us six different environments. Details of the study areas are shown in Table 1.
| Table 1: | Details of the description of the study area |
| Table 2: | Parental materials used in the study |
Experimental materials: The experimental materials consist of 10 parents (six introduced pure lines and four Ethiopian released varieties). Six were collected from Asian Vegetable Research and Development Center (AVRDC) located in Taiwan while the rest four local parental materials were collected from Melkasa Agricultural Research Center. Details of the parental materials are presented in Table 2.
Treatments, experimental design and field management: The experiment consisted of 45 F1 and 10 parents with a total of 55 genotypes. The experiment was laid out using RCBD with three replications. Field planting was done using plant spacing of 70×30 cm between rows and plants, respectively. All other recommended agronomic practices were employed during field management as recommended by Melkasa Agricultural Research Center (MARC).
Data collected: Data were collected from 10 randomly taken plants from each plot for yield, quality and other related traits. Plant height (cm), plant canopy width (cm), stem diameter (cm), branch number per plant, number of fruits per plant, fruit length (cm), fruit width (cm), fruit weight (g), fruit wall thickness (mm), number of seeds per fruit, total fruit yield (kg ha–1), total fruit dry weight (kg ha–1) and oleoresin content (w/w%) were studied.
Statistical analysis
Estimation of mid and better parent heterosis: Heterosis expressed as percent increase or decrease in the performance of F1 hybrid over the mid parent (average or relative heterosis) and better parent (heterobeltiosis) was computed for each character using the following equation18-20:
The significance of heterosis was tested with a t-test as specified below:
| = | Mean performance of better parent | |
| = | Mean mid parental value i.e.,., (P1+P2)/2 | |
| = | Mean performance of parent one | |
| = | Mean performance of parent two | |
| = | mean of F1 hybrid | |
| Me | = | Error mean square from ANOVA table |
| r | = | Number of replications. |
RESULTS
Mid and better parent heterosis: Heterosis and heterobeltiosis analyses for traits of interest were done for means combined over six environments. The over environment combined mean analysis confirmed that the magnitude of heterosis varied from -51.50% in fruit dry weight to 97.66% in fresh fruit weight. The combined mean analysis for heterosis over mid and better parent in percentage is presented in Table 3. The result substantiated that there were significant heterosis effects for the traits considered in the study. The heterosis was more magnified on yield and its components than growth traits in the study. Out of a total of 45 hybrids, 48.89 and 35.56% of crosses had shown mid parent heterosis and better parent heterosis in the desired direction, respectively. The current finding showed percentage mid parent heterosis in fresh fruit yield ranging from -38.63 to 97.66% for hybrids (Melkazala×Avpp0206) and (Melkashote×Avpp59328), respectively and that of better parent ranged from -47.24 to 80.44% for the same crosses. The result depicted that genotypes 24, 17, 23, 4, 32 and 41 were among the top crosses with highest heterosis and heterobeltiosis (Table 3, Fig. 1). In the case of dry fruit (pod) weight, the current finding revealed that mid parent heterosis varied from -48.09 to 61.69% and better parent heterosis ranged from -51.50 to 56.22% for crosses Melkazala×Avpp0206 and Melkashote×Avpp0105, respectively, in both cases. Out of the total, 48.89 and 42.22% of crosses had shown mid parent heterosis and better parent heterosis in the desired direction, respectively (Table 3).
| Table 3: | Combined mean percentage values of mid and better parent heterosis of yield and selected traits studied in hot pepper genotypes in 6 different environments, 2015 and 2016 |
PH: Plant height (cm), CW: Canopy width (cm), BN: Branch number per plant, FN: Fruit number per plant, FD: Average fruit diameter (mm), SN: Seed number per fruit, Yld: Fresh fruit yield (kg ha–1) and DW: Fruit/pod dry weight (kg ha–1), OL: Oleoresin content (w/w%), Mid (%): Percentage mid parent heterosis and Bp (%): Percentage better parent heterosis (heterobeltiosis) |
|
| Fig. 1: | Percent mid and better parent heterosis performance of fresh fruit yield (kg ha–1) for 55 hot pepper genotypes grown in six different environments, southern Ethiopia, 2015/16 |
Out of a total of 45 crosses, 53.33 and 31.11% of crosses had shown mid parent and better parent heterosis (Heterobeltiosis) in fruit length in the desired direction, respectively. Average heterosis of fruit length ranged from -21.63 to 32.93% for crosses 28 and 23, respectively, with a heterobeltiosis range of -25.18 to 28.64% for the same crosses. Fruit diameter has shown a heterosis range of -19.46 to 31.99% for crosses Melkazala×Avpp0512 and Melka awaze×Avpp9813. Heterobeltiosis had shown a range of -23.86 to 22.94% for crosses Melka awaze×Avpp59328 and Marakofana×Avpp59328. Of the total, 60 and 33.33% of crosses had shown mid parent heterosis and better parent heterosis superiority in the desired direction, respectively. Fruit number per plant showed significant heterosis for studied genotypes. The percentage heterosis over mid and better parent ranged from -37.56% (Avpp9813×Avpp0206) to 72.85% (Avpp9813×Avpp0514) and -43.92% (Avpp9813× Avpp0206) to 61.44% (Melka Awaze×Avpp59328), respectively (Table 3).
Plant height heterosis ranged from -17.21% (Marakofana×Melkashote) to 28.31% (Avpp9813× Avpp59328) and heterobeltiosis ranged from -24.49 to 19.86% for the same crosses. In general, 31.11 and 17.77% of the crosses showed mid and better parent heterosis in the desired direction. Branch number per plant had heterosis ranging from -18.30% (Marakofana×Melkashote) to 25.51% (Melkaawaze×Avpp9813) while heterobeltiosis ranged from -23.37% (Marakofana×Melkashote) to 10.32% (Melka awaze×Avpp0105). Of all the hybrids, 33.33 and 17.77% of crosses had shown mid and best parent heterosis in the desired direction (Table 3).
The oleoresin content results revealed significant superiority of some hybrids (crosses) in the desired direction for both mid and better parent heterosis. Mid parent heterosis ranged from -74.99% (Melka awaze×Marakofana) to 92.16% (Melkazala×Avpp59328) and that of heterobeltiosis ranged from -81.98 to 82.7% for the same crosses. Of the 45 hybrids, 48.89% showed positive mid parent heterosis while 35.56% had positive better parent haterosis. The genotypes 30, 33, 13 and 38 were among the best crosses or hybrids with highest heterosis and heterobeltiosis in the desired direction for further exploitation (Table 3, Fig. 2).
DISCUSSION
The result substantiated that there were significant heterosis effects varying from -51.50% in fruit dry weight to 97.66% in fresh fruit weight indicating crop potential of heterosis breeding for different traits for further improvement in the yield and quality. In fresh fruit yield, mid parent heterosis revealed a range of -38.63 to 97.66% indicating great genetic potential of genotypes for yield boosting by using F1 hybrids. This result agrees with Devi21, who indicated the marketable fruit yield average heterosis and heterobeltiosis varied from -20.36 to 113.19% and -22.94 to 102.93%, respectively. Most previous authors reported similar findings were Singh and Chaudhary22 reported heterosis that ranged from 7.40-33.24% for total fresh yield/plant, Kumar et al.23 reported heterosis ranging from 38.30-119.47 and 7.88-90.78% heterosis and heterobeltiosis, respectively, for yield/plant.
| Fig. 2: | Percent mid and better parent heterosis performance of oleoresin content for 55 hot pepper genotypes grown in 6 different environments, Southern Ethiopia, 2015/16 |
Similarly, mid and better parent heterosis in dry weight showed a range from -48.09 to 61.69% and -51.50 to 56.22%, respectively. Out of the total, 48.89 and 42.22% of the crosses had shown superiority in mid and better parent heterosis, respectively, in the desired direction which indicates a great genetic potential for exploitable heterosis. In line with the current finding, Gogula4 found that the average heterosis and heterobeltiosis for the 30 hybrids studied ranged from -32.47 to 68.93% and -36.35 to 64.77%, respectively. Moreover, other previous studies confirmed the superiority of this trait as observed by Sharma et al.24, Chaudhary et al.18, Hasanuzzaman et al.25, Medeiros et al.26.
Mid and better both parent heterosis in fruit quality such as fruit length and diameter were observed which substantiated the genetic potential of the crop for hybrid production for quality. Average heterosis of fruit length ranged from -21.63 to 32.93% and that of heterobeltiosis ranged from -25.18 to 28.64%. In agreement with the current result, Devi21 reported the range of heterosis from -8.63 to 148.32% and heterobeltiosis from -34.44 to 113.75%. Some earlier findings also confirmed similar results such as Burli et al.27 reported positive heterobeltiosis, 3.82 and 6.46%, for fruit length and number of fruits, respectively, Shankarnag and Madalageri28 observed heterobeltiosis of 9.16%, Singh and Hundal29 noticed heterosis over better parent in 55%, Gogula4 showed heterosis variation from -3.23 to 14.61% while heterobeltiosis variation from -10.02 to 8.08%. Again fruit diameter has shown a heterosis range of -19.46 to 31.99% and heterobeltiosis has shown a range of -23.86 to 22.94%. Of the total, 60 and 33.33% of crosses had shown mid and better parent heterosis in the desired direction. This result was in concordance with reports made by Shankarnag and Madalageri28, who observed that the extent of heterobeltiosis was 94.63%; Singh and Hundal29, who reported 24.48% heterobeltiosis for fruit width, again Davi21 reported the magnitude of heterosis for fruit width ranged from -30.78 to 13.67% and -39.89 to 7.47% over mid parent and better parent, respectively, Gogula4 observed the range of -8.06 to 16.27% heterosis and -10.53 to 12.94% of heterobeltiosis. The same were earlier reported by Sharma et al.24.
Fruit number per plant percentage heterosis over mid and better parent ranged from -37.56 to 72.85% and -43.92 to 61.44%, respectively, that again indicated the significant possibility to increase the yield in fruits by exploiting F1 hybrids. Consistent with the current result, the range of -8.63 to 148.32% and -34.44 to 113.75% over mid and better parent, respectively, were reported by Davi21. Other reports substantiated the current finding in such a way that Shankarnag and Madalageri28 observed 94.63% and Singh and Hundal29 66.55% heterobeltiosis for fruit number per plant. Again Gogula4 reported the range of -38.07 to 70.95% heterosis over mid parent and -46.56 to 41.47% over better parent.
The magnitude of heterosis and heterobeltiosis was relatively smaller in growth traits than yield and quality traits that gives an opportunity for immediate application of hybrid vigor for yield and quality improvement. In plant height, heterosis ranged from -17.21 to 28.31% and heterobeltiosis ranged from -24.49 to 19.86%. This is an indication for variability of genotypes for exploitation of heterosis in growth parameters of Capsicums. In line with the current finding, Singh and Hundal29 observed 37.22% heterobeltiosis for plant height. Similarly, branch number per plant had mid and better parent heterosis ranging from -23.37 to 25.51% and out of a total of 45 hybrids, 33.33 and 17.77% of crosses had shown mid and better parent heterosis in the desired direction, respectively. This also was in line with some previous researcher who reported both positive and negative heterosis and heterobeltiosis in branch number Patel et al.19 and Patil20.
Oleoresin content result revealed significant superiority of some hybrids (crosses) in the desired direction for both mid and better parent heterosis. Mid parent heterosis ranged from -74.99 to 92.16% and that of heterobeltiosis ranged from -81.98 to 82.7%. Of the 45 hybrids, 48.89 and 35.56% had positive mid and better parent haterosis, respectively, indicating the genetic potential of the crop for heterosis breeding for boosting oleoresin production. Consistent with the current investigation, Gogula4 observed the range of -5.22 to 47.10% relative heterosis and -11.65 to 35.79% heterobeltiosis in sweet pepper. Again Prasath and Ponnuswami30 and Ghosh and Pugalendhi31 reported range of -9.43 to 21.83% and -21.62 to 14.27% heterosis, respectively in chilli oleoresin that implies variation in magnitude of heterosis with genotypes tested.
CONCLUSION
There were superior F1 hybrids identified with varying magnitude of heterosis in all investigated traits. The top five selected crosses for mid and better parent heterosis include Melkashote×Avpp59328, Melkashote×Avpp0105, Marakofana×Avpp59328, Melka awaze×Avpp9813 and Avpp9813×Avpp0514 for fresh fruit yield and dry pod weight. Oleoresin content revealed significant superiority of some hybrids (crosses) in the desired direction for both mid and better parent. In most cases, the crosses superior in oleoresin were inferior in pod yield except a few. Thus, there is a need for critical evaluation of crosses for simultaneous breeding. Hence, the crop had immense potential for heterosis breeding for further improvement of its different traits.
SIGNIFICANCE STATEMENTS
In Ethiopia, improving hot pepper productivity (yield) is very crucial in order to benefit from pepper production. Hence, hybrid development is one of the best options to utilize the existing genetic variability to improve yield and quality.
ACKNOWLEDGMENTS
The authors would like to thank Wolaita Sodo University and Jimma University College of Agriculture and Veterinary Medicine for their valuable contribution in both facilitation and management support. Our recognition also extends to Melkasa Agricultural Research Center, especially the vegetable program staff, for their cooperation in providing planting materials and AVRDAC for the same. Moreover, our special thanks goes to Prof. Derbew Belew for his unreserved contribution for material transfer from AVRDC.