0731-B2
Rajni Chauhan 1
Dalbergia sissoo which is rated as a first class timber species is found to be quite variable in its morphology . In order to carry out improvement in the species it is prerequisite to have knowledge about its reproductive biology. Important observations like dehiscence of anthers, maximum pollen viabilty and receptivity in bud condition coupled with higher pod setting in controlled self pollinated individuals suggest that species is predisposed towards self pollination but simultaneously persisting of receptivity, pollen grains retaining viability even after opening of flower, some pod setting occur with cross pollination experiments suggest that we cannot rule out cross pollination in the species.
Dalbergia sissoo is distributed throughout the sub Himalayan tract usually up to 900m but sometimes ascending to about 1500m.It has been cultivated or self sown in the most parts of Indo-Pakistan sub continent for a long time. D. sissoo is a native of Indo-Gangetic basins and grows naturally in parts of Bhutan, Nepal, India and Pakistan. The tree has been introduced into many other countries like Java, Nigeria, Mauritius, Srilanka, Kenya etc. It is very likely that sissoo is indigenous to only the sub-Himalayan tract and has been introduced by man elsewhere.
In the natural habitat of sissoo maximum shade temperature varies from 39ºc to 49ºc and minimum from 4ºc to 6ºc. The normal rainfall varies from 760-4570mm.
In its natural state, Dalbergia sissoo grows most typically on alluvial ground either in the beds of river or mostly on the sand or gravel along the banks of rivers often very gregariously. Its preference is to a porous well irrigated soils with adequate moisture has been its characteristics feature wherever its growth has been a marked success. The tree is capable of existing in very poor soils, on hilly cliffs. It does not tolerate water logging. It is moisture-loving species
D. sissoo is recognised as an important multipurpose tree species. Its timber is used for making cabinets, veneers, bent wood articles like furniture, superior quality felloes for wheels, in gun carriage, in ordnance factories etc. It is also used for boat building, brush backs and to a small extent for unshielded bobbins. Considerable use in the sports equipments such as croquet, mallet heads and balls, as frames of tennis racquets cannot be disparaged. Sissoo wood is an excellent fuel, Seed oil and powdered wood is used for leprosy and skin disease treatment. Its wood is hard, heavy, strong, double elastic, seasons well and is decay resistant (Tewari 1994).
Sissoo is a deciduous tree often with crooked trunk and light crown. It fixes atmospheric nitrogen to ameliorate the site. Studies on reproductive biology and breeding systems are very important. It is the basic tool to carry out any future tree breeding programme. The breeding system, through the mechanism of reproduction, the method of pollination and the degree of compatibility, regulates the amount of recombination. The efficiency of reproductive system depends upon our understanding of factors affecting reproductive biology. To carry out any improvement programme it is desirable to collect all the information regarding the variability which is existing in the species with respect to the tree, flower, fruit, seed and even chromosomal level.
Methodology Surveys have been carried out in different agro-climatic zones of Punjab during flowering and fruiting period for consecutive three years from Oct1997-Dec 2000 to record various observations. Morphological variations were recorded during surveys through visual studies while cytological variations were known through preparation of meiotic slides by fixing the flowering buds in carnoy's fixative.
The complete data on the flowering chronology was recorded by visiting the marked 50 trees daily as soon as the deciduous phase was over. Data on following parameters was recorded.
Floral biology covering floral initiation, development, maturation, anthesis, receptivity, structure of flower, size of floral organs, pollen size, pollen structure, pollen germination. Nature of pollination was known through crosses made for self and cross pollination (Bangarwa 1996).
Pollination behavior was known through carrying out the pollination experiments separately for cross and self-pollination. Floral Biology, fruit biology and seed biology are studied in detail
These results were statistically compared by calculating the C.D at 5% level of significance.
A survey revealed that there exits a wide variation in the phenotypic characters of individuals selected for study. This variability has been categorised into different parameters as below.
During survey two morphotypes have been identified. Large variation was observed in leaf size, very small leaf size and large leaf size, Average size of leaves was recorded with scale manually. Leaves are imparipinnate, alternate with swollen base, rachis is 3.4- 9cms long. Leaflets are 3-5 in number with petiole 3.5-6mm in length. Small leaves have length 2.69±0.27 and breadth 2.19± 0.26 cm. The average length and breadth of larger leaves were observed to be 5.44 ± 0.28cm and 4.91± 0.22 cm, respectively These two types of trees were marked.
A wide range of variability was also observed for stem straightness and other morphological characters. Stem form ranged from branched or forked to completely straight trees.
Large variations was also seen in total tree height, clear bole height and girth at breast height, Girth at breast height and crown thickness. Average total tree height was 12.28±2.25 m. Cleanbole height 4.08±1.12 m, girth at breast height 105.67± 28.90 cm and crown thickness ranged from very light to very thick.
Branching pattern in D.sissoo ranged from upright branching to looping type pattern . The bark colour was recorded variable between brown to black .
Trees of D. sissoo largely varied for flowering intensity. Trees with very dense flowering and very thin flowering were also identified. Some differences in the flowering period of the trees was also observed. Some trees flowered earlier than others which can be due to change of environmental factors at different sites. Due to large variation in flower bearing capacity of trees, large variation in pod setting of trees was also observed. Trees which bear less flowers produced very less pods or even bears no pods and tree with very heavy flowering shows very heavy pod setting. Pods could be collected having 1 to 4 seeds.
This variation can be attributed to genetic makeup of the species along with different age and growing environment of the different trees.
Cytological variations The cytological studies on the species reveals that the chromosome number in the species is 2n= 20,i.e., it is diploid.
Phenology. Tree is leafless in December- January.The leaflets fall separately and before falling they turn brown. In the month of March-April, flowering starts along with the appearance of leaves.Flowering is influenced by temperature. High temperature hastens flowering. The whole process was completed in 15-20 days from bud initiation to flower opening. It takes 7-8 months from bud initiation to fully ripened pods. It was also seen that buds and flowers occur at the same time in different stages of development, even on the same branch of the tree.
Initiation 2nd week of March
Peak 1st week of April
Decline 4th week of April
It is observed that the inflorescence of D. sissoo is an axilliary panicle, composed of several short spikes with sessile to sub sessile flowers ranging from 7-14 in number per inflorescence. Length of inflorescence is recorded to be 3-8cms. Flowers Flowers of D. sissoo tree are small pea shaped, slightly fragrant with a fine toothed calyx ,five petals (including two narrow wings and a narrow keel) and are yellowish white in colour. Flower colour changed from yellowish white to orange after pollination. Androecium is composed of nine stamens that are united into a broad stalk, monoadelphous, stamens are in two sizes 5 large and 4 small. Length of all floral organs stamen, ovary, petals & sepal were measured to understand the pollination mechanism. It was found that average length of flower petals was 0. 9 ± 0.07 cm and lengths of stamens (0.79 ± 0.2cm) were slightly less than hairy pistil, which was measured to be (0.85± 0.06cm). The stalked hairy pistil has a narrow ovary containing 5-6 ovules, a short style and a dotlike stigma. In the bud stage the ovary is in bent form and surrounded by anthers. Anthesis Data on flower opening was recorded and it was found that maximum number of flower opening takes places between 10.00 hrs to 14.00 hrs with a peak between 11.30-13.30 hrs. It was also found that dehiscence of anthers also takes place in morning hours in the bud stage, just before flower opens.
Data was recorded on the opened flowers and unopened flowers, from this study, it was found that stigma becomes receptive few hours before flower opening and it was also noted that it remains receptive for few hours even after flowers opening. The stigma, which shows shiny and sticky surface, was considered as receptive.
Pollen grains were 3 zonocolpate, thin walled, spherical in shape having size 10.2um± 0.11um.
Pollen viability Viability of pollen grains was measured by the acetocarmine test. 2% acetocarmine solution was used to stain pollen grains on slides. Viability of pollen grains was studied at different stages of flower development. Maximum pollen viability 100% was found at bud stage before flowers opening which decreases considerably with storage.. This gives important information about the pollination pattern of the species. When the viability of the pollen grains was checked from the already opened flowers it was recorded to be quite low i.e., 56%. This highlights that the chances of the pollen to effect the fertilization are considerably low after the opening of the flowers.
To know about the mode of pollination the trees of the species were kept under constant observations for the visit of the insects and birds. It was seen that birds and insects do visit the flowers but do not participate in the pollination as they were found, when pollination had already taken place and flowers were in the stage of withering.
Self pollination. Under this experiment single bud inflorescence was selected before opening on each tree. 100 buds were bagged for selfing and data was recorded on pod setting. It was found that 16.25% pod setting occurs under controlled self-pollination. Some inflorescences were selected and tagged after counting the buds for recording pod setting percentage in nature, it was found that 35% pod setting takes place. Less pod setting under controlled self pollination with bagging is due to covering the buds with bags, which leads to the changed environment of the bud. Effective pollination is found to take place in the bud condition.
For this study young buds in which just corolla become visible were selected on the marked trees. These selected buds were emasculated early in the morning before 8.00 hrs. This process exposed the gynoeciums. After emasculation each bud was bagged to prevent contamination. On the same day at 11.00 to 12.00 hr the emasculated buds were pollinated with the pollens from other trees and again bagged. Data on pod setting was recorded and found that only 5-7% pod setting takes place.
Fruit Biology Pods mature in November-December. Pods were light brown and flat in shape. It has been seen that flowering and fruiting occurs simultaneously as young pods can be seen along with flowers on the inflorescences .
In natural pollinated inflorescences the number of pods/inflorescence ranged from 4-7.5 with a mean of 6.01 while in selfed ones it ranged from 3.2-4.5 with mean of 4.0.It is seen that the pods take about 6-7 months for complete maturity. The difference for mean number of pods per inflorescence between natural and self-pollinated inflorescence was significant.
The average pod length in natural pollinated inflorescence was 5.132 cm while in self-pollinated inflorescence it was 4.542 cm . The differences between and within the natural and self-pollinated tree for pod length were found to be significant.
In natural pollinated inflorescences the mean pod breadth was observed 7.420 mm while in selfed inflorescences it was measured to 7.40mm and in self pollinated individuals. Statistically self and natural pollinated individuals were found to be insignificant for this parameter, however, within the natural and self pollinated trees the differences were found to be significantly different.
100 pod weight The mean 100 pod weight in natural pollinated inflorescence was recorded and the range was found to be between 6.459-8.315gm with average of 7.055 gm and in self-pollinated pods it was found to be between 5.100- 6.425 with the average of 5.647 gm. These averages were found to be significantly different.
Pod is indehiscent in nature and remains on the tree for months together even after attaining the maturity. While this pod development is taking place, simultaneously seed development also occur inside the pod. There are 5-6 ovules/ovary . Thus depending upon the number of ovules fertilized the corresponding number of seeds develop inside the pod. The number is usually 1 to 4 seeds per pod . It is observed that the size of pod with one seed is smaller than the pod with 3 or 4 seeds. The seeds are initially green and the cotyledons are fully endospermic, they have the funicle attached to the pod wall. As they attain maturity the testa becomes hard and brown in colour and the dehydration of the seed takes place..
Seed Biology - Seeds of D. sissoo were observed to be light brown in colour flat and thin reniform in shape.
Seed Length - The mean length of one seed was observed to be 0.83 cm in natural pollination trees and 0.82 in self pollinated individuals, however, these differences were found to be insignificant..
Seed breadth - The mean seed breadth of one seed was recorded 0.42 cm in self as well as naturally pollinated individuals.
Seed weight - A sample of hundred seeds was taken to measure the seed weight. The average hundred seed weight of D. sissoo was recorded as 1.53 gms in the individuals which were self pollinated or naturally pollinated.
Seed germination - It is seen that there is no problem/ barrier i.e dormancy in seed germination and the germination percentage is very high in the fresh seeds i.e., up to 83.6 per cent in some trees. However, the mean seed germination percentage in naturally pollinated individuals is found to 73.68 per cent and in self pollinated individuals the value is 73.99 per cent. This reflects that there is no significant difference in the seed germination behavior of either naturally or self pollinated individuals. Within trees of both self or naturally pollinated individuals the differences in seed germination were found to be significant, which can be due to genetic makeup of the individuals .
Germination behavior - Germination begins on the third day of keeping the seeds on the moist petriplate and ends on the 6th day. Maximum germination is on the 4th day of setting up of the experiment .The germination is found to begin slowly i.e.!5-28% germination taking place on 3rd day while on the 4th day 40-55% germination takes place after this there is decline in the germination percent of the seeds. Effect of storage It is seen that the germination percentage remains very high even after one year of collection (85%-73%) i.e in the pods collected in the month of January the seeds retain the germination capacity up to coming month of January.
The differences in germination of seeds in the natural and self pollinated individuals is found to be statistically significant among the trees itself, which can be due the genetic constituent, age and the environment of the trees.
From the above studies following conclusions can be drawn
Thus, we can conclude that there is predominantly self pollination occurring in the species but we cannot rule out the chances of cross pollination occurring in the species simultaneously. Similar conclusions have been drawn by Bangarwa and Singh 1994.
Bangarwa KS and Singh VP (1994) Floral Biology and crossing techniques in Dalbergia sissoo Roxb In Dalbergia . Proc. of an International workshop.Ed. Westley SB and Roshrtko JM. Publ. Nitrogen fixing tree association, USA.
Bangrawa KS (1996). Sissoo Breeding. Publishers Agriculture and Forestry Information Centre. Hissar. India
Tewari DN (1994). Amonograph on Dalbergia Sissoo Roxb. International Book distributors, Rajpur Indiaa Road, Dehradun.India.
1 Department of Forestry and Natural Resources
Punjab Agricultural University
Ludhiana. (India).