EFFECT OF BAP, NAA AND GA3, EITHER ALONE OR IN COMBINATION, ON MERISTEM CULTURE AND PLANTLET ESTABLISHMENT IN SWEET POTATO (CV BRONDAL)

In Zimbabwe, the average sweet potato yield (6 t/ha) is relatively low when compared to Asian counterparts (17 t/ha). These low crop yields have been blamed on weevil infestations and viral infections which account for 60-90% of sweet potato yield losses in Africa. Meristem tip culture, a Centre for Potato Improvement (CIP) initiated tissue culture technique, has been widely used to eradicate viruses from clonally propagated crops and has been noted to be one of the instrumental techniques that helped China to increase sweet potato yields. In an effort to adopt the meristem tip culture technique for the production of virus-free planting material of a local sweet potato (cv Brondal), a study was conducted to evaluate the effect of Benzylamino purine (BAP), 1-Naphthaleneacetic acid (NAA) and Gibberellic acid (GA3) (either alone or in combination) on cultured Brondal meristems. The different hormonal treatments were assessed on the following parameters: plantlet regenerative capacity, multiple plantlet production, shoot height, average leaf number per shoot and average node number per shoot, ten weeks after meristem culture. All treatments containing a combination of BAP (1 mg-L) and GA3 (at either 5 mg-L, 10 mg-L, or 20 mg-L) had a significantly (p<0.01) higher plantlet regenerative capacity of 33-66% when compared to other treatment combinations. Only treatments, 10 mg-L GA3 + 1 mg-L BAP and 20 mg-L GA3 + 1 mg-L BAP were capable of inducing multiple plantlet formation, producing an average of three plantlets/meristem and two plantlets/meristem respectively. Overall, treatment 10 mg-L GA3 + 1 mg-L BAP gave rise to significantly (p<0.01) taller shoots (20 mm) compared to the rest of the treatments used. For average leaf number per shoot, all GA3 treatments (5 mg-L, 10 mg-L, or 20 mg-L) supplemented with 1 mg-L BAP gave significantly (p<0.01) higher numbers of leaves (six leaves/shoot) than the rest of the treatments. Treatments 10 mg-L GA3 + 1 mg-L BAP and 20 mg-L GA3 + 1 mg-L BAP gave rise to the highest number of nodes per shoot, producing an average of three nodes per shoot. In sharp contrast to treatments containing a combination of BAP and GA3, all treatments containing a combination of BAP and NAA performed poorly in all parameters tested for plant regeneration of Brondal sweet potato variety. In conclusion, the best hormonal treatment for culturing Brondal meristems proved to be 10 mg-L GA3 + 1 mg-L BAP.

Chemotaxonomic studies on Schwenckia americana LINN.

This study investigated the chemotaxonomic studies on Schwenckia americana Linn., a member of the family Solanaceae predominantly found mostly in low grass fields, Nigeria. The habit is annual herbaceous weed with slender stem characterized with free branching and growing up to 45cm in height.They are used mainly as medicine. The leaves are simple, entire, elliptic to ovate in shape, smooth, variable, petiolate and larger at the lower region of stem and narrowing to smaller almost sessile and oblanceolate towards the apical regions which are alternately arranged and acrescently structured from the top to the base upto 3.7 ± 1.5cm long and 2.4±0.6cm wide. The inflorescence is a panicle of 15 or more flowers occurring at stem terminal.The flowers are whitish tubular structures measuring up to 1.0±0.2cm in length and 0.1cm in diameter. The petals are whitish up to 0.9 ±0.2cm in length and sepals are greenish up to 0.1cm in length. The berry fruit is greenish when unripe and pale yellowish when ripe up to 0.3±0.1cm in diameter. The seeds are blackish and spherical or triangular shaped with rough edges measuring up to 0.1cm in diameter. The epidermal studies reveal anomocytic stomata whereas the trichomes are simple uniseriate forms wth bulge heads. The anatomy of mid-ribs and petioles showed bicollateral vascular systems. There are three vascular traces and the node is unilacunar. The petioles have 2 rib traces at primary growth phase. At secondary growth phase, the mid-rib and petiole revealed vascular arcs and the stem has a ring of open vascular system. The cytological studies showed a diploid chromosome number of 2n = 24 and n = 12 for the haploids. Alkaloids, saponins, tannins, phlobatannins, flavonoids, combined anthraquinones, free anthraquinones and cardiac glycosides are present.