STUDIES ON FLOWERING, POLLINATION AND FRUIT SET IN SOME APPLE CULTIVARS

A. Chauhan#, G. Sharma and K.K. Jindal

Department of Pomology, Dr. Y.S. Parmar University of Horticulture and Forestry,

Nauni-Solan 173 230, Himachal Pradesh

Introduction

Pollination is a very important and inseparable component in respect of regular and consistent production in a number of fruit crops. In a crop like apple, pollination is of utmost significance and its proportion and magnitude is primarily based upon appropriate selection of varieties. In a short span of about fifty years, apple cultivation has totally revolutionized the status of the farming community of Himachal Pradesh. Both production and productivity in the early phase of apple cultivation showed marked increasing trend but in recent times despite increase in area that is being brought under apple cultivation, corresponding increase in productivity is lacking. A number of factors are responsible, major being very old and declining orchards, lack of rootstocks, poor cultural practices, insufficient pollinators and poor selection of pollinizers.

In the last decade, there has been drastic changes in the climatic conditions. On account of strong micro climatic conditions, cultivars, as well as pollinizers, which were well adapted, have started showing variable responses. This has necessitated the urgency to select suitable cultivars and pollinizers for specific locations to sustain the declining trends in apple production and productivity. These view points were kept into consideration with the idea to identify some suitable pollinizers for delicious apple cultivars, which could resist the low productivity problem.

Materials and Methods

            Experiment was conducted during 2002 and 2003 at Regional Horticulture Research Station, Mashobra, Shimla (H.P.). For pollination eight pollinizers were taken namely Golden Delicious, Red Gold, Golden Spur, Tydeman’s Early Worcester, Granny Smith, Snow Drift, Golden Hornet and Manchurian. Data were recorded on flowering duration, flowering density, anther dehiscence, stigma receptivity in Delicious apple through fruit set under field condition, while pollen germination and pollen viability in Erythrosin B and Acetocarmine were observed in laboratory condition. Data presented is mean of two years observation. The observations on flowering were taken by recording the dates of starting of flowering, full bloom (75% flowers opened) and end of flowering. From these dates, the duration of flowering was worked out and expressed in days. Flowering density was recorded at pink bud stage, the length of the selected branches was measured and expressed as number of flower clusters per meter of shoot length (Lombard et al., 1988). For anther dehiscence fleshly opened flowers were selected and observations were recorded from 8:AM to 6:PM at interval of 2 hours. The percentage of anther dehiscence was calculated from total number of anther dehisced between 8:AM to 6:PM. Stigma receptivity was judged by artificially cross pollinating the emasculated buds of the different age groups with suitable pollinizer. After cross pollination, flowers were bagged and labeled. Stigma receptivity was determined by counting the number of fruitlet after three weeks of cross pollinations. Pollen viability was tested in 0.04%. Erythrosin B and Acetecarmine. In vitro pollen germination was done in sucrose solution of different concentration of 10, 15, 20 and 25%. The observations were recorded after 24, 48 and 72 hours in four to five microscopic field and average germination percentage in each cultivar was worked out.

Results and discussion

            It is revealed from the data (Table 1) that maximum flowering duration (16 days) was recorded in Snow Drift whereas, minimum duration (11 days) was recorded for  Golden Spur and Granny Smith Bist (1985), Sharma et al. (2005) and Sharma et al. (2006) reported that flowering duration in apple ranged from 10-17 days. Flowering density varied significantly among the pollinizers and varied from 12.32 to 33.48 clusters per meter. Snow Drift (Crab apple) recorded maximum flowering density (33.48 flower cluster/meter), which was significantly higher than other pollinizers whereas, minimum flowering density was observed in Tydeman’s Early Worcester (12.32 flower cluster/meter) which was statistically at par with Golden Delicious (13.58 flower cluster/meter) and Granny Smith (15.52 flower cluster/meter). The results are corroborated by the findings of Sharma and Gautam (2000). They reported that the Crab Apple had higher flower bud density in comparison to that of Golden Delicious. Stigma receptivity in Delicious Apple by visual observation observed during the period of study showed that stigma receptivity two days before anthesis ranged between 30.00 - 33.30% and between 66.67 - 68.33%. On the day of anthesis, receptivity was maximum varying between 83.30 to 85.00%, decreased to 65.00 - 66.67 and 40.00 to 43.30%, respectively one and two days after anthesis. Like wise stigma receptivity determined through fruit set method also indicated similar trend i.e., maximum fruit set was obtained the day of anthesis (37.90%) and least being registered two days both before (7.89%) and after anthesis (5.59%).

            Data pertaining to anther dehiscence revealed that amongst different pollinizers, highest percentage of dehiscence was recorded in Golden Delicious (20.08%) which was statistically at par with Red Gold (19.68%) and Snow Drift (19.85%). Minimum anther dehiscence was observed in Granny Smith (17.60%), which was at par with Golden Hornet (17.89%) Manchurian (18.05%) and Tydeman’s Early Worcester (18.26%). Pollen viability as determined by Erythrosin B test varied from 78.13 to 92.41%. The highest pollen viability in Erythrosin B was recorded in Red Gold (92.41%) followed by Golden Delicious (91.42%) and Granny Smith (89.03%) and lowest was observed in Golden Hornet (78.13%) when pollen viability was determined by Acetocarmine stain it ranged from 77.15 to 90.68%. Golden Delicious recorded highest pollen viability (90.68%) which was statistically at par with all other pollinizers except Golden Hornet and Manchurian whereas, lowest pollen viability was in Golden Hornet (77.15%) which did not differ statistically from Manchurian. The observation recorded on in vitro pollen germination of apple pollinizers in sucrose solutions at room temperature indicated that maximum pollen germination (69.97%) was found in Red Gold pollinizer irrespective of incubation period and sucrose concentration which was statistically better than any other pollinizers, on the contrary, significantly least value of 56.32% pollen germination was recorded in Golden Hornet.

            Pollen germination percentage increased significantly with the increase in incubation period from 24 hrs to 72 hrs irrespective of pollinizing cultivars. Difference in anther dehiscence and pollen viability among the pollinizers can be attributed to weather condition and the cultivars themselves. Variable genetic constitution of different cultivars in apple might be the reason for variation in pollen grain germination. Similar variation but in different cultivars and pollinizer at university of Horticulture and Forestry campus has also been reported by Sharma et al. (2005 and 2006).

            All the cultivars under study gave maximum pollen germination in 10% sucrose solution which appeared to be optimum as compared to 15, 20 and 25% sucrose solutions. In most of the cultivars under study an increase in sucrose concentration beyond 10% resulted in decreased pollen germination and the observation does not match with the observation of Sharma et al. (2005) who observed best pollen germination in 15% sucrose solution.

            Several workers have also studied the apple pollen germination in different sucrose concentrations. Kobel (1926) reported that 10-15% sucrose solution was optimum for apple pollen germination. However, Bist (1985) and Kumar (1996) obtained maximum pollen germination in most of the apple cultivars with 10% sucrose solution which is in conformity with the present findings.

            Pollination is an essential component in apple cultivation. The results in respect of time, duration of flowering, anther dehiscence are in line with the work of earlier workers (Kumar 1996, Sharma et al., 2005 and Sharma et al., 2006). The observations on pollen characters are in accordance with the earlier work (Sharma et al., 2006). The study of flower and pollen characteristic are very essential to manipulate and also in selecting a suitable pollinizer especially in a crop like apple where both production and productivity delicately balanced on the pollinizers. Through such studies suitable pollinizers for main cultivars under localized conditions would definitely play important role to sustain productivity.

Table 1: Flowering density, duration, stigma receptively, anther dehiscence and pollen viability in different

                pollinizers of apple

 References

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