Titus Magomere

Aims: The East African region is a centre of diversity for sorghum, there is need for studies on the role of interspecific hybridization and introgression of domesticated sorghum genes in weedy backgrounds. Study Design: Interspecific hybridization between S. bicolor and the weedy accessions belonging to S. halepense, S. sudanense and S. bicolor ssp. verticilliflorum accessions was studied. Methodology: At anthesis panicles of the weedy accessions were emasculated and pollinated with pollen from S. bicolor. The F1, F2 and BC1 populations were evaluated for simple sequence repeat (SSR) loci and phenotypic polymorphisms. Results: A range of alleles were observed across the assayed loci (2-8) including unique and null alleles. Shannon information content ranged from 0.2 to 1.98 on the loci, showing high polymorphism and genetic differentiation of the accessions used in the study. Alleles of between 70 and 300bp were obtained from all loci except loci SB1764, SB5058, SB3420, SB2389 and loci SB3258. Phenotypic analysis of S. bicolor, S. sudanense, S. halepense and their F1 progenies showed significant variation on vegetative traits. S. sudanense had greater number of tillers (3.3), number of branches (0.3), total seed number (3010) and photosynthesis (110); S. bicolor had a higher 100 seed weight (3,1g) while S. halepense had the least flowering (65,1%) but more ratooning (3.8). In contrast to their parental species, the F1s had profuse tillering (2.3 - 3.4), were taller (121- 144 cm) and had more seed (2814 – 3243). The crosses had mid way clusters between respective parents in ssr loci dendogram analysis. A 3:1 and 1:1 segregation was observed in the F1 and BC1 populations respectively. Conclusion: F1 populations were obtained between S. halepense x S. bicolor and S. sudanense x S. bicolor. There is need for more studies on the role of crop to non-crop hybridization within the species.

BACKGROUND: Maize production in Africa is hindered by a myriad of biotic challenges, key among them being invasive and native lepidopteran stemborers. Recent invasion of the continent by fall armyworm, Spodoptera frugiperda , has further exacerbated the situation. Fortunately, Cotesia icipe was found to be very promising against S. frugiperda . However, the co‐occurrence and interaction between S. frugiperda and the stemborers ( Busseola fusca , Sesamia calamistis , and Chilo partellus ) in maize agroecosystem may jeopardize the efficiency of C. icipe as a biocontrol agent of S. frugiperda . This study investigated the performance of C. icipe on S. frugiperda , Spodoptera littoralis and the stemborers. Specifically, the preference and acceptability of C. icipe to the host insects, the physiological suitability of the hosts for its development, and the effect of these hosts on the fitness parameters of the offspring were assessed. RESULTS: Cotesia icipe accepted all the tested hosts, albeit with higher preference for Spodoptera species than for stemborers under multiple‐choice tests. Also, the highest parasitism of up to 97% was recorded on S. frugiperda compared with parasitism on the stemborers of 43% in B. fusca . Moreover, physiological suitability and fitness traits (except for per cent female offspring) varied with host species, again being optimal on Spodoptera species. CONCLUSION: Cotesia icipe demonstrated strong potential to control S. frugiperda in maize due to its high affinity for parasitization and developmental success in this host; and despite its non‐specific parasitization, the presence of other hosts may not prevent its maximum control of S. frugiperda . © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Polyploidy was induced in Melia volkensii (Mukau), a valuable native tree from the semi-arid regions of East Africa. Cotyledons of diploid M. volkensii (2n = 2x = 28) were treated with oryzalin for 0 (control), 1, 2, or 3 h with or without pretreatment with 1.1 µM thidiazuron. Cotyledons treated with 10 mg·L⁻¹ oryzalin for three hours yielded 40% tetraploids. Pretreatment of cotyledons with thidiazuron for 18 days followed by treatment with oryzalin increased tetraploid plant production to 52.5%, but this also yielded more mixoploids. Compared to diploid M. volkensii, the tetraploid in vitro and young potted plants were compacter, with thicker stems, wider leaves, and a low density of longer and wider stomata. In the coming years, tetraploid M. volkensii plants will be observed in field trials and serve as a basis for further breeding efforts.

Before in vitro propagated Melia volkensii plants can be used for mass planting, the transition phase to in vivo conditions needs to be better controlled because too many plants are lost during acclimatization and in the field. Two experiments were set up to evaluate the effects of biological agents on the establishment of M. volkensii in vitro plantlets. The biological agents consisted of Trichotech^®, Bio-cure B^®, Rhizatech^®, Bacillus subtilis, a Trichoderma isolate and self-isolated native arbuscular mycorrhizal fungi (AMF). Regarding the latter, in soil from the nursery, the number of AMF spores increased from six spores to 400 per 100 g of soil using a trap culture, in which thirteen AMF morphotypes were identified and root colonization assessed through observation of hyphae, vesicles, coils and appressoria. The first experiment was set up in the greenhouse to investigate the efficacy of the biological agents on the hardening off. In the second, a field experiment was set up to study their effect on the early establishment of the plantlets in the field compared to seedlings. All biological agents significantly (p ≤ 0.05) improved in vitro plant survival and growth compared to the control. The highest plant height and number of leaves per plant were recorded in plants treated with Rhizatech^®, Native AMF, Bio-cure B^® and Trichoderma isolate. The treatments with Rhizatech^®, Bio-cure B^® and native mycorrhiza recorded a significantly wider stem. The root diameter of the plants treated with Rhizatech^® and Bio-cure B^® was the largest, but the plants inoculated with the native AMF had the longest roots. Moreover, the inoculated plants generally developed multiple secondary roots. After two months, AMF had clearly colonized the acclimatized plantlets. In the field experiment, the biologicals made no difference in survival rate but did produce a significantly larger leaf area after two months, with the largest leaves recorded with Rhizatech^®, native AMF and Trichotech^®. They also increased the quality index of the plants from 0.21 to 0.52. The performance of in vitro grown M. volkensii plants six months after planting in semi-arid conditions in Kiambere was better than that of seedlings. Inoculation of plants increased plant height and diameter. Thus, inoculation of biological agents is an efficient approach for improving the early growth of in vitro propagated M. volkensii plants.