Crossing eficiency studies in Mandarin varieties

Introduction

Citrus is the main fruit crop in the world and third most important fruit crop in India next to mango and banana. Citrus spp. is perennial in nature and which comprises of mandarin, sweet orange, lime, lemon, grapefruit, pummelo, citron, etc. contributes great economy in many citrus growing countries. Among various cultivated citrus species, mandarin groups contribute 43% share, followed by sweet orange (25% share), acid lime & lemons with 25% and others with 7% share. The Mandarin orange, which is also known as mandarin is the common type of orange that is widely cultivated in Nagpur. Nagpur mandarin is the most popular fruit among all types of oranges in India due to its sweet-sour appealing taste and easy peelable quality of the rind. The oranges are famous for their sweet and juicy pulp and were given the Geographical Indication (GI) tag in 2014. GI tag 385 identifies the Nagpur orange as being one which has "a specific geographical origin and possesses qualities or a reputation that is due to that origin". Study of crossing eficiency of diferent varieties is an essential prerequisite for initiating hybridization programme. Besides, the knowledge of the flower behavior, pollination, fruit set and fruit development will be highly useful in undertaking the problems involved in the poor fruitfulness in many varieties of citrus. A perfect knowledge of pollen fertility, stigma receptivity, pollen germination, pollen size, number of crosses done, crossing success, fruit setting and F1seed germination is essential pre-requisite for initiating programme of breeding. It is also useful in taxonomical studies. Citrus plants hybridize easily between species with completely diferent morphologies, and similar-looking citrus fruits may have quite diferent ancestries. Most commercial cultivars are the product of hybridization among these wild species, with most coming from crosses involving citrons, mandarins and pomelos. Keeping this in view, the present investigation entitled, "Crossing eficiency Studies in mandarin varieties." was planned and undertaken with objectives to study the crossing eficiency in diferent mandarin varieties.

Material and Methods

The present experiment entitled "Crossing eficiency studies in mandarin" was conducted at Regional Fruit Research Station, Katol and Centre of Excellence for Citrus, Nagpur, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola during Ambia bahar (February, 2022). The experimental material consisted of five varieties of citrus group i.e., Nagpur mandarin, Nagpur seedless, Minneola, Beauty of Glen Retrate and Butwal.. These five varieties were used for crossing to produce 10 direct and 10 reciprocal crosses to study the crossing eficiency and to collect the crossed seeds. Unopened mature flower buds from the pollen parents were collected and after removal of petals and stigma, flowers were kept under light for 12-16 hours for pollen dehiscence one day before pollination. Flowers of selected parents were emasculated in the evening of the day before pollination. Pollination was done by applying pollens with camel hair brush or simply by touching anthers on the sticky surface of stigma of the mother parent. After satisfactory pollination, the pollinated flowers were covered with butter paper bag and labelled with tag writing the date and name of parent. As the technical program, observation was recorded on pollen fertility, stigma receptivity, pollen germination, pollen size, number of crosses done, crossing success, fruit setting and F1seed germination was recorded. The design adopted in the experiment was Randomized Block Design (R.B.D.) with twenty crosses and four replications.

Results and discussion

Pollen fertility (%) Significant variation in pollen fertility was observed among diferent mandarin varieties as presented in Table 1. Significantly maximum pollen fertility was noted in Minneola (89.04%) which was statistically at par with Nagpur seedless (87.62%), whereas minimum pollen fertility was recorded in Butwal (66.80%) and it was significantly lower than other varieties. These findings were confirmed by Hassan et al. (2008) [1] who observed that, the variety Celiopatra, Sayed Marri, El-shorbagee and Sonbol showed the highest pollen fertility.

In order to find out the receptivity of stigma, pollination of the flowers was done at various period. The data with respect to stigma receptivity is presented in Table 1. Stigma receptivity was maximum (4-5 days) in Beauty of Glen Retrate and Nagpur mandarin, whereas, minimum stigma receptivity was recorded in Nagpur seedless, Minneola and Butwal (3-4days) each. Maximum stigma receptivity was observed on the day of anthesis. Similar results were obtained by Singh and Dhuria (1960) [2] who studied floral biology of sweet lime. He found that, the stigma receptivity lasted for 6 days and was at maximum at the time of flower opening.

Significant variation in Pollen germination was observed among diferent mandarin genotypes Table 1. Significantly maximum pollen germination was recorded in Nagpur mandarin (64.83%) which was statistically at par with Beauty of Glen Retrate (59.65%) and Nagpur seedless (56.27%), whereas significantly minimum pollen germination was recorded in Butwal (45.79%) and it was significantly lower than other varieties. These findings was found similar given by Singh and Dhuria (1960) [2] . He observed that, the percent germination of pollen was upto (51.24%).

Pollen size (µm)

The Pollen size was observed among diferent mandarin varieties and presented in Table 1. Significantly maximum pollen size was recorded in Beauty of Glen Retrate (31.68 µm) which was statistically at par with Butwal (30.10 µm), Minneola (29.51 µm) and Nagpur mandarin (29.76 µm), whereas minimum pollen size was recorded in Nagpur seedless (25.59 µm) and it was significantly lower than other varieties. These findings were confirmed by Khan et al. (2021) [3] who studied floral biology and phenology in Sweet orange and observed that, the pollen size of this variety was measured as (27.75 µm).

Crossing eficiency Number of crosses done

The data regarding number of crosses done was presented in Table 2. Total 20 crosses were done, out of which 10 were direct crosses and 10 were reciprocal crosses. More than 900 crosses were done as per availability of flowers in the season. Out of which maximum crosses were done in Nagpur mandarin x Nagpur seedless (86) from direct crosses, whereas Nagpur seedless x Nagpur mandarin (78) in reciprocal crosses.

The data regarding success in crossing was presented in [5] who observed that, the fruit set percentages were highest in cultivar Jafa under open pollination (32.84%) followed by self-pollination (29.81%).

References

1. Hassan NA, El-Halwagi AA, Khalaf RM, Sayed HA, ElHomosany AA. Morphological characterization, pollen grain feritility and some chemical characters of selected mandarin (Citrus spp.) varieties. Arab. Univ. J. Agric. Sci. 2008;16(1):161-177.
2. Singh JP, Dhuria HS. Studies on floral biology of sweet lime. (Citrus limettoid Tanaka). Indian J. Hort. 1960;17(2):9-20.
3. Khan MAH, Rahim MA, Rabbani M, Hassan MF, Haque MA. Studies on floral biology and phenology in sweet orange (BARI Malta-1) under subtropical condition of Bangladesh. Plant Archives. 2021;21(2):459-464.
4. Jaskani MJ, Khan IA, Khan MM. Fruit set, seed development and embryo germination in interploidal crosses of citrus. Scientia Horticulture. 2005;107:51-57.
5. Kumatkar RB, Godara AK, Sharma VK. Studies on floral biology and breeding behaviour of Sweet orange [Citrus sinesis (L.) Osbeck.]. The Bioscan. 2016;11(1):543-546.