INHERITANCE OF RESISTANCE TO SESAME GALL MIDGE IN UGANDA

Sesame gall midge, caused by Asphondylia sesami Felt, is an important constraint to sesame ( Sesamum indicum L. ) production in Uganda. Few genotypes have been reported on sesame gall midge, especially hairy genotypes. However, for genetic improvement, there is need to understand the mode of resistance to sesame gall midge in these genotypes. Thirty sesame genotypes were screened for gall midge resistance, under field conditions at Ngetta Zonal Agricultural Research development Institute (ZARDI) in northern Uganda. The spreader row technique was used in order to increase insect pressure on the tested genotypes. The half diallel method 2, model 1 was used to cross 5x5 parents. The result showed that non-additive gene action was important in the inheritance of resistance to sesame gall midge. Cross analysis showed that the GCA x site and SCA x site interactions were significant (P< 0.05), indicating that the additive and non-additive gene actions simultaneously controlled the inheritance for the resistance. The estimate of heritability in narrow sense genetic coefficient of determination (analogue heritable proportion) showed that the resistance was not highly heritable. Estimates of GCA and SCA effects suggest that the parent, Local158, was the best combiner for resistance to gall midge; while the parent AjimoA1-5 was the poorest combiner for the trait. Crosses Local158 x 7029-1-2 and Sesim1 x AjimoA1-5 were the best for the resistance to sesame gall midge. The estimates of genetic effects for resistance to sesame gall midge, showed predominance of additive and additive x additive type of epistasis in the inheritance of the resistance, though dominance also had a role in the cross Sesim1 x 7020-1-2.La c\ue9cidomyie du sesame, caus\ue9e par Asphondylia sesami Felt, est une contrainte majeure \ue0 la production du s\ue9same ( Sesamum indicum L. ) en Ouganda. Tr\ue8s peu de g\ue9notypes r\ue9sistants \ue0 la c\ue9cidomyie de s\ue9same ont \ue9t\ue9 enregistr\ue9s, en particulier les g\ue9notypes \ue0 pubescence. Cependant, pour une am\ue9lioration g\ue9n\ue9tique, il est n\ue9cessaire de comprendre le mode de r\ue9sistance en jeu. Trente g\ue9notypes de s\ue9same ont \ue9t\ue9 \ue9valu\ue9s en plein champ pour la r\ue9sistance \ue0 la c\ue9cidomyie de s\ue9same, \ue0 Ngetta, Institut Zonal de Recherche D\ue9veloppement en Agriculture (ZARDI) au nord de l\u2019Ouganda. La technique d\u2019\ue9pandage en ligne a \ue9t\ue9 utilis\ue9e dans le but d\u2019accroitre la pression d\u2019insecte sur les g\ue9notypes test\ue9s. La m\ue9thode2, mod\ue8le 1 de croisements diall\ue8le sans r\ue9ciproques a \ue9t\ue9 utilis\ue9e sur 5x5 parents. Le r\ue9sultat montre que l\u2019action non additive des g\ue8nes est tr\ue8s importante dans l\u2019h\ue9r\ue9dit\ue9 de la c\ue9cidomyie de s\ue9same. L\u2019analyse des croisements a montr\ue9 que l\u2019habilet\ue9 combinatoire g\ue9n\ue9rale (GCA) et l\u2019habilet\ue9 combinatoire sp\ue9ciale (SCA) montrent varient de fa\ue7on significative d\u2019un site \ue0 un autre (P< 0.05), ceci indique que l\u2019effet additif et non additif des g\ue8nes contr\uf4lent l\u2019h\ue9r\ue9dit\ue9 de la r\ue9sistance \ue0 la c\ue9cidomyie de s\ue9same de fa\ue7on simultan\ue9e. L\u2019\ue9valuation de l\u2019h\ue9ritabilit\ue9 au sens strict a montr\ue9 que le caract\ue8re r\ue9sistant n\u2019est hautement h\ue9ritable. L\u2019estimation des effets de GCA et SCA sugg\ue8re que le parent Local158, \ue9tait le meilleur combineur pour la r\ue9sistance \ue0 la c\ue9cidomyie de s\ue9same, tandis que le parent AjimoA1-5 \ue9tait le pire combineur. Les croisements Local158 x 7029-1-2 et Sesim1 x AjimoA1-5 \ue9taient les meilleurs pour la r\ue9sistance \ue0 la galle de s\ue9same. Les estimations des effets g\ue9n\ue9tiques pour la r\ue9sistance \ue0 la c\ue9cidomyie de s\ue9same a montr\ue9 la pr\ue9dominance d\u2019\ue9pistasis de type additive et additive x additive dans l\u2019h\ue9r\ue9dit\ue9 de la r\ue9sistance \ue0 la galle de s\ue9same, bien que la dominance aussi joue un r\uf4le dans le croisement Sesim1 x 7020-1-2

Segregation of hydroxycinnamic acid esters mediating sweetpotato weevil resistance in storage roots of sweetpotato

Resistance to sweetpotato weevils, (Cylas spp.) has been identified in several sweetpotato (Ipomoea batatas) landraces from East Africa and shown to be conferred by hydroxycinnamic acids that occur on the surface of storage roots. The segregation of resistance in this crop is unknown and could be monitored using these chemical traits as markers for resistance in F1 offspring from breeding programmes. For the first time in a segregating population, we quantified the plant chemicals that confer resistance and evaluated levels of insect colonisation of the same progeny in field and laboratory studies. We used a bi-parental mapping population of 287 progenies from a cross between I. batatas ‘New Kawogo’, a weevil resistant Ugandan landrace and I. batatas ‘Beauregard’ a North American orange-fleshed and weevil susceptible cultivar. The progenies were evaluated for resistance to sweetpotato weevil, Cylas puncticollis at three field locations that varied climatically and across two seasons to determine how environment and location influenced resistance. To augment our field open-choice resistance screening, each clone was also evaluated in a no choice experiment with weevils reared in the laboratory. Chemical analysis was used to determine whether differences in resistance to weevils were associated with plant compounds previously identified as conferring resistance. We established linkage between field and laboratory resistance to Cylas spp. and sweetpotato root chemistry. The data also showed that resistance in sweetpotato was mediated by root chemicals in most but not all cases. Multi-location trials especially from Serere data provided evidence that the hydroxycinnamic acid esters are produced constitutively within the plants in different clonal genotypes and that the ecological interaction of these chemicals in sweetpotato with weevils confers resistance. Our data suggest that these chemical traits are controlled quantitatively and that ultimately a knowledge of the genetics of resistance will facilitate management of these traits, enhance our understanding of the mechanistic basis of resistance and speed the development of new sweetpotato varieties with resistance to sweetpotato weevil

Novel agmatine derivatives in Maerua edulis with bioactivity against Callosobruchus maculatus, a cosmopolitan storage insect pest

Food security in developing countries is threatened by crop pests and ectoparasites in livestock. Strategies for their management still rely on synthetic pesticides which are not always effective and the active ingredients persist in the environment with negative consequences for beneficial arthropods, farmers and consumers, hence necessitating research on sustainable alternatives. Botanical insecticides are increasingly relevant, typically having lower impacts on users, consumers and the environment. One example is the southern African shrub the Blue bush-berry, Maerua edulis. Recent work reported effective pest control using this plant species against cattle ticks, storage beetles and vegetable pests. However, little is known about the chemistry underlying activity and this is essential to optimize its use. Here, we identified two novel plant chemical tructures, the E and Z isomers of cinnamoyl-4-aminobutylguanidine along with the E and Z isomers of 4-hydroxycinnamoyl-4-aminobutylguanidine in the leaves of M. edulis. We isolated these compounds from the leaves and elucidated their chemical structures using various spectroscopic techniques including High Resolution Mass Spectrometry and Nuclear Magnetic Resonance Spectroscopy. We also identified a further 11 closely related structures of which 6 are tentatively reported here for the first time. Stachydrine and 3-hydroxystachydrine were also identified in the leaf extract, and occurred at very high concentrations; up to 2% w/w of dry leaves. We tested these two compounds, along with the 4 main cinnamoylamides and the crude M. edulis leaf extract against the cowpea bruchid Callosobruchus maculatus at concentrations equivalent to those present in extracts used by smallholder farmers. Mortality of insects exposed to crude plant extracts after 72 h was significantly higher than the untreated control although still lower than for insects exposed to rotenone, the positive control. The two new compounds and stachydrine showed similar activity to the crude extracts suggesting that these compounds explained the activity of the extract. After 6 days, the mortality of insects exposed to crude extracts and isolated compounds was similar to that recorded with the positive control. The stachydrine fraction and the E and Z isomers of cinnamoyl-4-aminobutylguanidine also inhibited oviposition activity in fecund female beetles. Our data show that methanol extracts of M. edulis were toxic to C. maculatus and inhibited oviposition even at 0.1% w/v so these foliar chemicals may explain the activity of the plant material. We also synthesized the amides which facilitated structural elucidation, produced adequate quantities for testing and demonstrated the potential for commercial synthesis

Identification of simple sequence repeat markers for sweetpotato weevil resistance

The development of sweetpotato [Ipomoea batatas (L.) Lam] germplasm with resistance to sweetpotato weevil (SPW) requires an understanding of the biochemical and genetic mechanisms of resistance to optimize crop resistance. The African sweetpotato landrace, ‘New Kawogo’, was reported to be moderately resistant to two species of SPW, Cylas puncticollis and Cylas brunneus. Resistance has been associated with the presence of hydroxycinnamic acids esters (HCAs), but the underlying genetic basis remains unknown. To determine the genetic basis of this resistance, a bi-parental sweetpotato population from a cross between the moderately resistant, white-fleshed ‘New Kawogo’ and the highly susceptible, orange-fleshed North American variety ‘Beauregard’ was evaluated for SPW resistance and genotyped with simple sequence repeat (SSR) markers to identify weevil resistance loci. SPW resistance was measured on the basis of field storage root SPW damage severity and total HCA ester concentrations. Moderate broad sense heritability (H2 = 0.49) was observed for weevil resistance in the population. Mean genotype SPW severity scores ranged from 1.0 to 9.0 and 25 progeny exhibited transgressive segregation for SPW resistance. Mean genotype total HCA ester concentrations were significantly different (P < 0.0001). A weak but significant correlation (r = 0.103, P = 0.015) was observed between total HCA ester concentration and SPW severity. A total of five and seven SSR markers were associated with field SPW severity and total HCA ester concentration, respectively. Markers IBS11, IbE5 and IbJ544b showed significant association with both field and HCA-based resistance, representing potential markers for the development of SPW resistant sweetpotato cultivars

Effects of hydroxycinnamic acid esters on sweetpotato weevil feeding and oviposition and interactions with Bacillus thuringiensis proteins

Sweetpotato weevil (SPW) pest management is challenging because the pest target is sub-terranean, so the application of pesticides is impractical and usually ineffective. Host plant resistance and the genetic transformation of sweetpotatoes to produce entomotoxic Bt proteins offer potential for environmentally benign pest control. Resistance can be conferred by naturally occurring hydroxycinnamic acids which protect against oviposition by adults, but these compounds are restricted to the root surface so do not protect against the cortex bound larvae where the greatest damage occurs. Resistance could be enhanced if combined with expression of Bt proteins in transformed plants but interactions between hydroxycinnamic acids and Bt proteins remain unknown. Here the bioactivity of Cry7Aa1 protein and hydroxycinnamic acid esters was evaluated individually and in combination against SPW larvae and mortality determined. Low and high concentrations of hydroxycinnamic acid esters alone caused significantly higher mortality of both weevil species in all experiments compared to the control. SPW larval mortality was greater when tested as a combination of hydroxycinnamic acid esters and Bt protein but this effect was additive not synergistic. Although we report no evidence of antagonistic interactions the antifeedant effects of the plant compounds conferring host plant resistance could have reduced consumption of the Bt protein in our assays leading to a lower efficacy when combined. Further work is required to determine if the toxic effects of Bt proteins function alongside host plant resistance in sweetpotato under field conditions

Phytochemical mediated resistance in sweetpotato to sweetpotato weevils

This study evaluated sweetpotato resistance to sweet potato weevils (Cylas spp.) and investigated the phytochemicals that mediated this defence. New Kawogo, LIR302 and ARA228 were shown to be the most resistant based on stem and root damage. Significant differences were observed on the number of faecal droppings, feeding holes and eggs laid on the root in a choice and no-choice bioassays confirming that New Kawogo, LIR302 and ARA228 affected development and emergence of adult weevils. Six hydroxycinnamic acid esters, including hexadecylcaffeic, hexadecylcoumaric, octadecylcaffeic, octadecylcoumaric, heptadecylcaffeic and 5-O-caffeoylquinic acid esters were identified on the root surface and amounts of these differed significantly between resistant and susceptible varieties. The mean number of C. puncticollis and C. brunneus feeding holes, faecal droppings and egg laid on the root core were significantly different among the root cores treated with synthetic hydroxycinnamic acid esters. The study also showed that there were significant differences in the root volatiles of resistant and susceptible variety both before and after infestation. The larval survival of sweetpotato weevil was significantly affected by hydroxycinnamic acid esters treatment and Bt-toxin applied on the diet. There was also significant differences in percentage sweetpotato weevil root infestation among genotypes of the segregating population. The genotype by environment (GxE) interaction effect was also significant on the sweetpotato weevil damage on the stem portion of the sweetpotato vine indicating that weevil stem damage is dependent on the season. The mean number of sweetpotato weevil feeding holes differed significantly on the root of the genotypes of the segregating population in the feeding and oviposition bioassay. There was significant difference in total hydroxycinnamic acid (HCA) esters among the genotypes of the segregating population. The distribution of genotype mean total HCA ester concentration was skewed to the left and only one progeny, NKB257, had higher total HCA ester concentration than New Kawogo, the resistant mother used in the crossing. A weak but significant correlation between total HCA ester concentration and sweetpotato weevil root damage was observed signifying that resistance to sweetpotato weevils depended on other factors as well. The results are discussed in terms of how they might be incorporated into integrated pest management of sweetpotato weevils

Inheritance of Sclerotinia Midstalk Rot Resistance in Elite Sunflower Breeding Germplasm NonCommercial-NoDerivatives 3.0 License. (CC BY-NC-ND 3.0) Publication History

Abstract Sclerotinia sclerotiorum (Lib.) de Bary is a yield-limiting factor and the major disease of sunflower (Helianthus annuus L.) in the temperate regions of the world. In this study, we characterized resistance to S. sclerotiorum midstalk rot and morphological traits in a population derived from a cross between two Sclerotinia resistant lines. Phenotypic data for 114 F3:4 lines and the two parents, NDBLOSsel and K04, were obtained under artificial infection in field experiments which yielded moderate to high heritabilities. Our results suggest that S. sclerotiorum resistance is highly quantitative and that different genomic regions may mediate the resistance in different tissues of the plant. We found transgressive segregation for all three resistance traits suggesting that both resistant parents carried complementary QTL. In addition, we investigated the segregation of two known QTL for midstalk resistance and found that one of them also acts as a major QTL in this cross between two resistant lines. Collectively, our results suggest that a QTL stacking approach is a promising way to increase resistance to S. sclerotiorum in elite sunflower germplasm

Segregation of Hydroxycinnamic Acid Esters Mediating Sweetpotato Weevil Resistance in Storage Roots of Sweetpotato

Resistance to sweetpotato weevils (Cylas spp.) has been identified in several sweetpotato (Ipomoea batatas) landraces from East Africa and shown to be conferred by hydroxycinnamic acids that occur on the surface of storage roots. The segregation of resistance in this crop is unknown and could be monitored using these chemical traits as markers for resistance in F1 offspring from breeding programs. For the first time in a segregating population, we quantified the plant chemicals that confer resistance and evaluated levels of insect colonization of the same progeny in field and laboratory studies. We used a bi-parental mapping population of 287 progenies from a cross between I. batatas ‘New Kawogo,’ a weevil resistant Ugandan landrace and I. batatas ‘Beauregard’ a North American orange-fleshed and weevil susceptible cultivar. The progenies were evaluated for resistance to sweetpotato weevil, Cylas puncticollis at three field locations that varied climatically and across two seasons to determine how environment and location influenced resistance. To augment our field open-choice resistance screening, each clone was also evaluated in a no choice experiment with weevils reared in the laboratory. Chemical analysis was used to determine whether differences in resistance to weevils were associated with plant compounds previously identified as conferring resistance. We established linkage between field and laboratory resistance to Cylas spp. and sweetpotato root chemistry. The data also showed that resistance in sweetpotato was mediated by root chemicals in most but not all cases. Multi-location trials especially from Serere data provided evidence that the hydroxycinnamic acid esters are produced constitutively within the plants in different clonal genotypes and that the ecological interaction of these chemicals in sweetpotato with weevils confers resistance. Our data suggest that these chemical traits are controlled quantitatively and that ultimately a knowledge of the genetics of resistance will facilitate management of these traits, enhance our understanding of the mechanistic basis of resistance and speed the development of new sweetpotato varieties with resistance to sweetpotato weevil

Analysis of sesame seed production and export trends; challenges and strategies towards increasing production in Uganda

Sesame (Sesamum indicum L.) is one of the most ancient oilseed crops cultivated for its edible oil and uses in food. Sesame seeds are very nutritious and confer health benefits. However, its potential production in Uganda has not been fully realized. The objective of this review was to summarize the trends in sesame production, export quantity, export value, challenges, and strategies for sustainable sesame seed production in Uganda. The review revealed the sesame seed production and area harvested generally increased from 1996 to 2007 but significantly decreased between 2008 and 2018. The review also revealed that while the export quantities and values were low, they gradually increased from 2009 to 2016. The decreased production between 2008 and 2016 could have been due to challenges such as pests and diseases, loss of soil fertility, prolonged drought, poor agronomic practices, poor yielding varieties, and lack of access to credit. Therefore, it is recommended to improve breeding programs and soil management practices; strengthen agricultural credits and extension services to support marketing of sesame seeds; and improve agronomic practices and farmer knowledge on improved techniques such as sowing methods, plant spacing, intercropping practices, pests and disease control measures. These could boost sesame production in Uganda given the high domestic and global demand for sesame seeds and provide an opportunity to expand sesame production throughout Uganda. Research should focus on how to increase seed yield on farmers’ fields and bridge the yield gap between researchers and farmers while adopting good agronomic practices

Control of origin of sesame oil from various countries by stable isotope analysis and DNA based markers--a pilot study.

The indication of origin of sesame seeds and sesame oil is one of the important factors influencing its price, as it is produced in many regions worldwide and certain provenances are especially sought after. We joined stable carbon and hydrogen isotope analysis with DNA based molecular marker analysis to study their combined potential for the discrimination of different origins of sesame seeds. For the stable carbon and hydrogen isotope data a positive correlation between both isotope parameters was observed, indicating a dominant combined influence of climate and water availability. This enabled discrimination between sesame samples from tropical and subtropical/moderate climatic provenances. Carbon isotope values also showed differences between oil from black and white sesame seeds from identical locations, indicating higher water use efficiency of plants producing black seeds. DNA based markers gave independent evidence for geographic variation as well as provided information on the genetic relatedness of the investigated samples. Depending on the differences in ambient environmental conditions and in the genotypic fingerprint, a combination of both analytical methods is a very powerful tool to assess the declared geographic origin. To our knowledge this is the first paper on food authenticity combining the stable isotope analysis of bio-elements with DNA based markers and their combined statistical analysis