Evaluation of elite clove (Syzigium aromaticum (L.) Merr. and Perry) accessions and standardization of pollination techniques

Abstract

The present study entitled “Evaluation of elite clove (Syzigium aromaticum (L) Merr. & Perry) accessions and standardization of pollination techniques” was taken up with the specific objective to evaluate elite clove accessions and to standardize pollination techniques for hybridization.

The twelve elite accessions identified from estates of Trivandrum and Kollam districts of Kerala designated as BRC-1, BRC-2, BRC-3, BRC-4, MRC-5, MRC-6, MRC-7, MRC-8, AMC-10, AMC-11, AMC-12 and AMC-13 were evaluated during the period of 2018-2020. Quantitative characterization was done with 25 quantitative characters including tree, leaf, bud, flower, yield, fruit and seed characters. The girth of the tree at 30 cm height was maximum in BRC-3 (165 cm). Highest number of inflorescence/m2 was recorded in AMC-12 (156.25). The number of flower buds/inflorescence was maximum in MRC-6 (17.25) while single bud fresh and dry weight was highest in BRC-3 with 398.72 mg and 127.26 mg respectively. The mature bud length among the clove accessions was the maximum in BRC-1 (19.34 mm) whereas the mature bud diameter was maximum in BRC-3 (6.45 mm). The dry bud yield per tree was the highest in MRC-7 (8.13 kg) followed by BRC-1 (7.48 kg). Quantitative characters summarized based on the descriptive statistics revealed wider range of variability in single bud weight fresh, number of inflorescence/m2, single bud weight dry and girth of the tree.

Multi Dimensional Scaling (MDS), a multivariate analysis done on 25 variables with 12 observations revealed 10 dimensions and the contribution of MDS Dimension-1 and Dimension-2 were 75.76 and 17.21 percent with cumulative variance of 92.97 percent respectively. Based on the scree plot of MDS, first 2 dimensions were selected for generating the biplot. Based on MDS configuration eight clusters of selected clove accessions were identified. Dendrogram representing the relationship among 12 elite accessions based on Euclidean distance also identified same eight clusters of clove accessions that identified in MDS configuration. The linkage analysed based on the biplot of two dimensions of multidimensional scaling of biplot coordinates revealed a strong positive association between most of the characters measured except, girth at 30 cm height, number of inflorescence per m2, single bud weight fresh and single bud weight dry. Minimum Data Set for identifying a promising clove accession generated revealed accessions BRC-1, MRC-5 and MRC-6 had better ideotype and can be suggested as elite or superior accessions.

The experiment on floral phenology and biology was carried out in clove plants at Braemore estate, Trivandrum district. The flower opening time of the clove flowers observed were between 2:30-6:30 pm. However the percentage of flower opened was maximum between 3.30- 5.30 pm. The number of stamens per flower varied from 167 to 343. The rupturing of anthers started 36 hours before anthesis and maximum anther dehiscence occurred between 36 h before anthesis till anthesis. The pollen grains were monad, radially symmetrical, triangular, trizonosyncolporate and were having exine ornamentation. The polar diameter of pollen grain ranged from 17.06-18.22 µm and the equatorial diameter of pollen grain ranged from 19.40-20.70 µm. The stigma receptivity by hydrogen peroxide test revealed stigma receptivity was there upto six days from anthesis and maximum stigma receptivity was observed on fifth day of anthesis with highest number of bubbles (31.40 per cent). The emasculation should start from 48 hour before flower bud opens which was revealed by the starting of separation of the petals since anthers started rupturing from 36 hour before anthesis.

Pollen viability by iodine potassium iodide method revealed that pollen viability was maximum at 12 hour before anthesis (94.02 per cent). Pollen fertility was also maximum on the pollen collected 12 hour before anthesis (82.83 per cent). Thus the pollen collection should be undertaken 12 hour before anthesis. Pollen collected and dried at 50°C and stored upto two months of storage in refrigerator had maximum pollen viability whereas pollen fertility was maximum in pollen dried at 50°C and stored in desiccator. The hybridization was carried out on selected five clove plants as male and female parents. The percentage of fruit set ranged from 15 per cent to 42.5 per cent and average fruit set from all the plant combinations was 28.87 per cent.

The study on “Evaluation of elite clove (Syzigium aromaticum (L) Merr. & Perry) accessions and standardization of pollination techniques” revealed that clove accessions such as BRC-1, MRC-5 and MRC-6 had superior ideotype and superior in effective yield. The floral phenology of clove was studied and pollen collection, storage and artificial hand pollination in clove was standardized.