Comparative Study Of Seeds And Seedlings Characteristics Of Acacia senegal Acacia mellifera And Acacia laeta

Abstract

Comparative Study of Seeds, Seedlings Characteristics of A.senegal, A.mellifera and A.laeta

Elhag Elbashier Musa

The objective of this study is to find the easy methods for distinguishing between seeds of A.senegal, A.mellifera and A.laeta. This is because there is a confusion in collecting seeds of A.laeta with seeds either of A.senegal or A.mellifera. Based on this confusion, the study aimed to support the hypothesis that there are two morphological forms of A.laeta, one is very similar to A.mellifera, which is considered as Shubahi Kitir, and the other is very similar to A.senegal which is considered as Shubahi Hashab. According to the above mentioned confusion, this work is concentrated on comparative study of pods, seeds and seedlings characteristics of A.senegal, A.mellifera and their Shubahis. The study includes the similarities and differences between the four mentioned trees in their pods parameters (length, width, full and abortive seeds per pods), seeds characteristics (length, width, thickness and etc. . ), numbers of seed per kilogram and herbarium specimens were collected for leaves and leaflets measurement. All these measurements were done at National Tree Seed Center Soba. A natural seed source of Elmazmum is representing the location of this study. It is spreading a cross the gum belt with rainfall varied from 300-600mm per annum. Pods of each type were collected from not less than 10 trees, at least a hundred meters apart from each other. After seed cleaning, parts of seeds of A.senegal, A.mellifera and their Shubahis were stored in ventilated containers (cotton bags) at room temperature 30± 5ºC and relative humidity 45-55% (normal store). And other parts of the same species were stored in an air tight containers (drum, small Jerican) in a cold store at (12± 1ºC) and relative humidity 55-65% for 18 months. The moisture content and germination of the stored seeds were checked every 3 months. The imbibition rate of seed was calculated daily after soaking in water for 8 weeks. Also the traits of seedling growth were measured for 3 ages at one-month interval. The results of this work were analyzed statistically using ANOVA followed by Tukey Kramer range test for mean variation. The study showed significant differences between A.senegal, A.mellifera and their Shubahis in their leaves and leaflets, Shubahi Kitir tree has long leave length followed by Shubahi Hashab, A.melliefra and A.senegal respectively. And then A.melliferra tree has long and wide leaflets, followed by Shbahi Kitir , Shubahi Hashab and A.senegal respectively. The study showed considerable differences between A.senegal, A.mellifera and their Shubahis in their pods parameters and seed characteristics. A.senegal has longer pod and big seed than the other species, while A.mellifera has shorter pods and smaller seeds than the other. But the two Shubahis have intermediate pod and seed parameters dispersed between those of A.senegal and A.mellifera. Seed viability of A.senegal, A.mellifera and their Shubahis was tested by cutting and tetrazoilum test. They showed no significant differences between A.senegal, A.mellifera and their Shubahis in seed viability. Germination rate showed no significant differences between the treated and untreated seed of A.senegal, A.mellifera and their Shubahis during the 12 months of storage, but after this period, a significant dropping appear in seed viability A.senegal, A.mellifera and their Shubahis. During the storage period ,A.mellifera seed has top germination rate which followed by A.senegal , Shubahi Kitir and Shubahi Hashab respectively. A.senegal, A.mellifera and their Shubahis showed no significant differences in moisture content during the storage period. The imbibition of seed of A.senegal, A.mellifera and their Shubahis with soaking in water showed two strategies of two groups of species. The first group is represented by A.senegal and Shubahi hashab, while the other group is represented by A.mellifera and Shubahi kitir. This high imbibitions indicates that, A.senegal, A.mellifera and their Shubahis have physical dormancy (thin -coated seed) and it can be overcome by soaking in water. Significant differences were observed between A.senegal, A.mellifera and their Shubahis in shoot length during seedling growth rate. These results showed that the two Shubahis, seedlings are fast growing than A.mellifera and A.senegal seedling. Irrigation regimes did not give significant differences between A.senegal, A.mellifera and their Shubahis in their shoot length and fresh and dry weight of seedlings, but they have considerable effect on their root length. Therefore the irrigation once every two weeks gave the higher value of root length, followed by once a week and twice a week irrigation regimes respectively. This illustrate that, the root length and biomass production increased with seedling age and water scarcity (water stress). No significant differences were observed between A.senegal, A.mellifera and their Shubahis in branches and leave number of seedlings. And also, no significant differences were recorded between A.senegal, A.mellifera and their Shubahis in root fresh and root dry weight. The irrigation regimes have no significant effect on root weight and root dry weight at the first age (one month), but they have significant effect on root fresh and dry weight of seedlings of A.senegal, A.mellifera and their Shubahis at the second and third age (Two and three months). The once every two weeks regimes of irrigation gave the highest value of root biomass, while the twice a week regimes gave the lowest value. The study also showed no significant differences between A.senegal, A.mellifera and their Shubahis in nodules number at the first and second age (two months), while significant variation was appears at the third age (3 months). The two Shubahis gave bigger number of nodules while the smallest number was obtained by A.senegal throughout the age time (3 months). Therefore, the nodulation increased with seedling age and biomass production. The study showed significant differences between A.senegal, A.mellifera and their Shubahis in the shoot to root ratio at the third age (3 months), but at the first and second age (one and two months) did not appear. Shoot to root ratio was high at the first age, while it decreased with time (ages). This results confirm the fact that was highlighted by Ledig, (1983), woody species where shoot to root ratio decrease with age, this may be due to the allocation of more nutrients to root system than shoot system. The study showed an index of similarities percentage in morphological characters between A.senegal, A.mellifera and their Shubahis, which are shown below: A.senegal with Shubahi Hashab = 53% A.senegal with Shubahi Kitir = 47% A.senegal with A.mellifera = 58% A.mellifera with Shubahi Kitir = 53% A.mellifera with Shubahi Hashab =58% Shubahi hashab with Shubahi Kitir =58% Considerable recommendations were drawn from this work it is recommended that further studies are needed on: taxonomy (chemo, cytology..etc), genetic,anatomoy (seed and timber ). Separate plantations of each of A.senegal, A.mellifera and their Shubahis are recommended and seed orchard could be established for tree improvement in case of gum production.