Agronomic performance and phenotypic variability of the F2 population derived from various types of okra varieties

Okra is a functional vegetable with high nutrient content and medicinal value potential. Evaluating genetic material from various genetic sources is a standard procedure in plant breeding programs. A field study was carried out to evaluate the agronomic traits of F2 populations derived from various types of varieties and assess the phenotypic variability of the traits. The research was conducted at the Research Station of the Faculty of Agriculture, Andalas University, from January to May 2021. The materials used are seeds from self-pollinated of 16 F1 populations with various varieties, i.e., hybrid, composite, introduced and local varieties. Data was collected based on an individual observation, and the data were then analyzed using descriptive statistics. Results showed that the entire population of the F2 derived from both hybrid or composite varieties, introduced or local varieties, has diverse agronomic traits, indicating their potential to be developed as parental inbred lines. All agronomic traits evaluated showed wide variability, indicating a high possibility to obtain plants with valuable and desirable traits. The exception was found for the optimum picking time; however, the optimum picking time 7, 8 or 9 DAA is sufficient to obtain fruit with higher fruit weight and fruit size.


Introduction
Okra (Abelmoschus esculentus (L.) Moench) is a vegetable crop consumed in immature and tender texture fruit.Okra is known as okro or gumbo in Java, and bende or bendhi in Malaysia belongs to the family Malvaceae.The fruit is capsule-shaped or pod and contains numerous seeds [1].In Indonesia, this vegetable is relatively new, and usually, this commodity is founded in a hyper-market.
Okra pod is a functional food with high nutrient content and medicinal value potential [2].Its pod consists of protein, fat, carbohydrates, vitamins, minerals and fibre [3,4], indicating the importance of okra in the human diet.The tender pod contains high-level antioxidants [5].The pod characteristic is mucilage in most pod parts and potential as anti-cholesterol [6] and anti-diabetic [7,8].Okra seeds are potentially anti-fatigue as the polyphenols and flavonoids content [9], while its oil has a hypocholesterolemic effect [10].
Okra has originated in tropical Africa and is now widespread worldwide [11,12].Several okra cultivars have been introduced for years, then widely adopted in Indonesia.The origin and types of cultivars are a source of genetic material for plant breeding programs.The genetic source can be used as selected materials to improve the characteristics of the crop [13].Inbreeding with selection is used as standard produce parental inbred lines in a hybrid breeding program.Evaluation of the agronomic performance suggests which particular plants developed as variety and which particular traits should be improved.This study aimed to evaluate the agronomic traits of F2 populations derived from various types of varieties and assess the phenotypic variability of the traits.

Materials and Method
This research has been carried out in the Research Station, Faculty of Agriculture, Universitas Andalas, Padang, in West Sumatra province, Indonesia, located at 175 m above sea level.Rainfall during research ranges from 104.8 -392.7 mm/month, while daily temperatures range from 24 -29.5 o C.
The genotypes evaluated in this research consisted of 16 different F2 populations.Seeds are derived from self-pollinated hybrid or composite cultivars (Table 1).The color of young pod and pod type were determined based on IBPGR [1].The number of plants evaluated varied from 3 -20 due to their survival throughout the evaluation.The experimental plot size was 250 cm x 120 cm, covered with mulch plastic.The plot consists of two rows with 60 cm x 40 cm spacing for inter-and intra-row.Fertilizer dose and its application are similar to those reported by [14].All agronomic practices followed as per standard recommendation.The observation of the yield component was carried out based on the highest frequency for the optimum picking time.The optimum picking time criteria are the maximum day of fruit picking when the fruits still have a tender and non-fibrous texture [14].Phenotypic characterization of okra referred to the okra description guideline by IBPGR [1] and UPOV [15].Data collection was conducted based on an individual observation, and then data were analyzed using descriptive statistics.The observed variables were plant height, first flowering time, the total number of fruits, fruit set percentage, the maximum picking time, pod weight, pod diameter and pod length.When the variance of the traits was more than two times of standard deviation, the phenotypic variability was classified as wide [16].

Results and Discussion
Flowering time, plant height, the number of pods per plant, pod weight, pod length and pod diameter of 16 F2 populations have a diverse performance, indicated by a considerable standard deviation value in almost all traits (Table 2 & 3).High variability within the population indicates that the composition of the genotypes controls the trait in each F2 population varies.The value of germplasm depends on the number of accessions, and upon the diversity present [17].Each population in the F2 generation consists of plants with different genotypes depending on the allele segregation resulting from the inbreeding process.The variability in each population for each trait in the F2 generation is essential for crop improvement.The magnitude of variability indicates a high opportunity to select the particular traits within the population.Plants with desirable traits can be developed as parental inbred lines.
Plant height among the population in the F2 generation varied (Table 2).Performance of the F1, derived from introduced and local cultivars, has been evaluated previously by [14], indicating a decrease of an agronomic trait in the F2.The reduction in plant height occurred in all populations, ranging from 16.9 -77.5% for the plants derived from the F1 hybrid varieties and 10.2 -49.4% for the plants derived from the composite variety.The decrease in height indicates the occurrence of inbreeding depression in plant height.Inbreeding depression phenomenon existed on plants derived from genetically heterozygous plants (F1 hybrid or composite cultivars).Even though okra is potentially a self-pollinated crop, pollinator insects bring on out-crossing [5].The existence of inbreeding depression in okra has been reported by [18,19].
In contrast, the first flowering time of plants in the F2 generation is faster than that of the F1 by 4 -12 days, while it is longer for okra Merah and okra Hijau cultivars by five days.Lucky5, VN-1 and Ve-022 become the top three genotypes with a high number of pods per plant, indicating their ability to produce a high yield.The percentage of fruit sets of the F2 population ranged from 38.4 -92.3%, indicating the different genotype responses to set a pod.The high number of fruits/plant and fruit set are desirable and become the critical indicators to assess the genetic potential of crop yields.Based on the trait variability among plants within a population, VN-1 is highly likely to produce the highest yield (15.5±10.2pods) with a relatively moderate fruit set (76.2%).The optimum picking time of plants within the population varied (Table 3).The difference in the optimum harvest time determines the quality of okra fruit.The longer the optimum harvest time, the greater the weight and size of the fruit [20].However, when the fruit is harvested exceeding the optimum harvest time, the quality of the fruit decreases.The texture of the fruit is hard and fibrous, so it is not suitable anymore for consumption as a vegetable.
Fruit weight, fruit diameter and fruit length of the F2 population showed a considerable variation in values.The variation is due to the difference in genetic and fruit picking time.The differences are also caused by the time of fruit trait observation differences.Differences in fruit characteristics were also observed between the F2 and the F1 populations.The time for picking fruit in the F1 population was at 8 DAP, while the picking time for the F2 population was at a maximum picking time of 8 or 9 DAP.The exception was for okra Merah and okra Hijau cultivars which are harvested at 7 DAP both for the F1 and F2 populations.Extended picking time from 7 to 8 or 8 to 9 DAP increased weight, diameter and length of fruit.All the fruit harvested at optimum picking time revealed values within the range of the hardness measurement as reported by [2] using a force gauge, i.e. 3.20 -8.08 Newton, indicating the tenderness texture of pods.
The variability of agronomic traits in 16 F2 populations shows a wide value in all traits, except the picking time trait (Table 4).Wide variability indicates the magnitude of the opportunity to obtain plants with a particular trait.Wide variability also specifies that selecting the particular trait is more effective and efficient.Thus the possibility of success in the selection breeding program is high, and the crop improvement program will be rewarding.The optimum picking time ranges from 7, 8, or 9 DAA; hence the trait showed narrow variability.Okra fruit is commonly consumed at 5-10 DAA [21]; hence, extending the picking time to 7, 8, or 9 DAA is sufficient to obtain fruit with a higher yield, viz.higher fruit weight and fruit size than fruit that is picked earlier.

Conclusion
The entire population of F2 which was derived from both hybrid, composite varieties, introduced, and local varieties have diverse agronomic traits, indicating their potential to be developed as parental inbred lines.All agronomic traits evaluated showed wide variability, indicating a high possibility to obtain plants with valuable and desirable traits.The exception was found for the optimum picking time; however, the optimum picking time 7, 8 or 9 DAA is sufficient to obtain fruit with higher fruit weight and fruit size.Further studies to evaluate the self-pollinated of this F2 population need to be carried out to obtain the inbred lines.

Table 1 .
Population, fruit character, seed source origin and type of variety

Table 2 .
Plant height, flowering time, the number of flowers and fruit set of various F2 populations * DAP = Days after planting

Tabel 3 .
The optimum picking time, fruit weight, fruit length and fruit diameter of various F2 populations The number in the bracket is the percentage of plants harvested on 7, 8 or 9 DAA.# The data used is the fruit harvested on picking with the highest frequency.Data used for Ve-045 was picked at 8 DAA.

Table 4 .
Variability of the agronomic traits of 16 F2 population