Median Development Period Research Articles

Influence of rice grain traits to their susceptibility to the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera, Bostrichidae)

Rice grains of 20 varieties were tested for their physical and biochemical basis of resistance against lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera, Bostrichidae). Physical parameters such as grain length x breadth, thousand seed weight, and grain hardness exhibited significant differences among tested varieties. Grain hardness conferred resistance significantly by resulting in delayed adult emergence (-0.519), and weight loss per cent (-0.603). Biochemical parameters such as total carbohydrates and proteins showed significant differences among the varieties. Total carbohydrate was positive and significantly correlated with adult emergence, but with median development period negatively correlated. Protein content was also found positively correlated with adult emergence and negatively correlated with the median development period.

Physical Attributes of Wheat Varities in Relation to <i>Rhyzopertha dominica</i> (F.)

This study aims to explore the susceptibility of wheat varieties in storage against Rhyzopertha dominica (F.). Twenty promising wheat cultivars were tested for resistance in non-choice conditions at the Department of Entomology, MSSSoA, Odisha during 2021-22. The wheat varieties were premeditated for their physical components through correlation analysis and the level of influence on insect preference and development was determined. The variety DBW303 which had a high median development period, low adult emergence and susceptible index was found to be resistant. Similarly, the variety PBW373 which recorded a low median developmental period with higher adult emergence, and susceptible index, was found to be susceptible. Among the physical traits, varieties with grain hardness exhibited a negative relationship with progeny development and thus conferred resistance.

Susceptibility of pro-Vitamin A biofortified maize genotypes to Sitophilus zeamais (Mots) in Ghana

Pro-Vitamin A Biofortified maize is one of the crops with the cheapest and most sustainable option for preventing Vitamin A deficiency in humans in Ghana. It is also a key energy component of feed for layer chicken, forming about 60-70% of the total feed. Sitophilus zeamais is one of the most serious primary internal feeding pests of maize and other grains in sub-Saharan Africa. It causes both quantitative and qualitative grain losses. Two no - choice laboratory experiments in 112 days cumulative feeding of S. zeamais and 60 days susceptibility of six pro-Vitamin A Biofortified Maize (PVABM) genotypes to the insect were conducted. The experimental designs were Completely Randomized Design in four replications. Percentage grain damage and weight loss were significantly lower (P<0.05) in Aburokokoo than the other genotypes. Significantly more S. zeamais emerged from Accession GH2354 which also had significant (P<0.05) higher percentage grain damage than other genotypes. In the 60-day susceptibility experiment, grain hardness had significant (P<0.05) negative correlation with F1 progeny, index of susceptibility and protein content but positive significant correlation with median development period. Large number of S. zeamais F1 progeny, high susceptibility index, high protein, low total carbohydrate content, short median development time with low grain hardness value were observed on accession GH2354. Aburokokoo had significantly (P<0.05) small number of F1 progeny, low index of susceptibility, low protein and high total carbohydrate, long development period and intermediate value of grain hardness. The ascending order of grain hardness among the maize genotypes was GH2354<Obatanpa <Aburokokoo<Abontem<Honampa<Ahoodzin. There was no relationship between grain length, width and thickness and grain susceptibility. A cluster dendrogram obtained from the maize genotypes with regard to resistance parameters to S. zeamais showed that accession GH2354 and Obatanpa-QPM were susceptible, Ahoodzin, Honampa and Abontem were moderately resistant, with Aburokokoo resistant to the maize weevil infestation. Key words: Biofortified maize, stored produce, insect pest, Vitamin A deficiency, grain damage

Resistance to Callosobruchus maculatus among cowpea (Vigna unguiculata (L.) Walp) genotypes

ABSTRACT Callosobruchus maculatus is an important field-to-store pest that causes close to 100% losses in stored produce. This study aimed at assessing the resistance of cowpea genotypes to C. maculatus infestation. Thirteen cowpea advanced breeding lines pre-selected on the basis of their high grain yield, and three released varieties (Padi-tuya, Kirkhouse Benga and Wangkae) were evaluated in a no-choice experiment. The experiment was laid out in a completely randomized design with four replications under laboratory conditions. Data were collected on mean number of eggs per seed (MEPS), days to first emergence (DFE), adult bruchid emergence (ABE), percentage weight loss (PWL), percentage seed damage (PSD) and median development period (MDP). Dobie’s susceptibility index (DSI) was computed and used to classify the genotypes as resistant or susceptible. Significant differences were found among the genotypes for the measured traits, except for DFE and MDP. IT13K-1070-2 had the lowest MEPS, ABE, PWL and PSD. C. maculatus, with high ABE, developed best on Kirkhouse Benga and Wangkae. Wangkae had 100% seed damage at the end of the experiment. Based on the DSI score, IT13K-1070-2 was found to be moderately resistant; the rest of the genotypes were susceptible. Among the susceptible genotypes, IT10K-817-3, IT07K-303-1, SARI-2-50-80, SARI-3-11-100, IT10K-837-1, IT13K-1424-12 and SARVX-09-004 had PWL of less than 16%, indicating tolerance to bruchid infestation. DSI was significantly and positively correlated with ABE (r = 0.81), PSD (r = 0.93) and PWL (r = 0.79). DSI had a significant negative correlation with the final seed weight (r = −0.83). IT13K-1070-2 could serve as a useful source of resistance to the cowpea bruchid in cowpea breeding programs or released as a variety for cultivation.

Application of multi‐locus GWAS for the detection of bruchid resistance loci in cowpea (Vigna unguiculata)

AbstractIdentification of genes associated with bruchid resistance variations in cowpea accessions would help breeders to generate new cowpea cultivars with improved resistance and quality. In this work, 107 cowpea collections from various areas in six countries were phenotyped for their responses to Callosobruchus maculatus and genotyped with Single Nucleotide Polymorphism (SNP) markers. Six multi‐locus models Genome Wide Association Study (mrMLM, FASTmrMLM, pKWmEB, pLARmEB, FASTmrEMMA and ISISEM‐BLASSO) were used to associate the genotype data to phenotypic cowpea resistance traits: Percentage of Bruchid Emergence (PBE); Percentage of Weight Loss (PWL); Median Development Period (MDP); Dobie Susceptibility Index (DSI); Number of Egg Laid (NEL) and Mean Number of Hole (MNH). Out of 14 QTNs, three were associated with more than one trait and were associated with 11 candidate genes located within 10–30 kb of the QTNs. These candidate genes exhibit functionalities associated with cowpea resistance mechanisms. All these results could contribute to the gene networks in resistant cowpea varieties. The result of this study could also increase our knowledge of genetic resistance of cowpea to bruchids and could be useful for molecular breeding.

Inheritance and combining ability estimates for cowpea resistance to bruchid (Callosobruchus maculatus Fab.) in Benin cowpea

Cowpea bruchid (Callosobruchus maculatus Fab.) is the most important storage pest causing significant economic losses. Development of bruchid resistant cowpea varieties is the most sustainable strategy for controlling bruchid. However, information regarding the nature of gene action governing the resistance to bruchid is limited for cowpea genotypes in Benin. This study aimed to understand the genetic basis of cowpea resistance to C. maculatus. Eight parents were crossed in a full diallel mating design. 56 F2 progenies were tested with the eight parental genotypes in alpha lattice design with three replications in laboratory. Data were recorded on bruchid emergence (BE); weight loss (WL); median development period (MDP); Dobie susceptibility index (DSI); number of eggs laid (NEL); average number of holes (ANH); seed damage (SD). Combining ability analysis was performed using Griffin's method 1, model 1 in AGD-R software. The results showed that general combining ability (GCA) effects were highly significant (p < 0.001) and negative for BE, WL, DSI, NEL, ANH, and SD on the parents. Significant positive GCA effects were observed for MDP. Thus, the parents TVU13677, IT84S2246-4, WC36 and WC66*5T were the best combiners for bruchid resistant. High narrow sense heritability was observed for BE (0.75), WL (0.69), DSI (0.72), ANH (0.77) and SD (0.69). These results showed that both additive and non-additive gene action govern the resistance to bruchid in cowpea. The genotypes (TVU13677; IT84S2246-4; WC36; WC66*5T) and the resistant crosses were the promising genotypes and can be used in breeding programs seeking to develop bruchid resistant cowpea varieties. • Cowpea is a major source of dietary protein in Sub-Saharan Africa. • Bruchid is the most important storage cowpea pest causing significant losses. • This study evaluated the Inheritance of C. maculatus resistance in cowpea. • The hopeful cowpea genotypes useable in breeding programs were found.

Breeding for Weevil (Sitophilus Zeamais Motschulsky) Resistance in Maize (Zea mays L)

A study was conducted with an overall objective of establishing the determinants of weevil resistance in maize. Field experiments were done at GART using a North Carolina Design II with three replications and also at Nanga research in Mazabuka. Laboratory experiments were conducted at Zambia Agriculture Research Institute (ZARI) Entomology laboratory and University of Zambia, Food Science Department where insect bioassay and the biochemical tests were done respectively. In the insect bioassay grain hardness, grain weight loss, median development period, F1 progeny emergence and the Dobie index of susceptibility indices were measured. Protein and the Phenolic content were determined under the biochemical tests among genotypes. They were highly significant differences in all the twenty seven genotypes evaluated. Results showed that Parental survival accounted for 78.5 % of the total variation, Phenolic content was strongly and positively correlated (r = 0.423***) with grain hardness providing a good measure of resistance accounting for the 10.9 % of the total variation. The study showed the possibility of breeding maize genotypes with an increased resistance and also susceptible lines had a decreasing Phenolic content but increasing Phenolic content resulted in increased resistance. It was therefore concluded that Phenolic content and parental survival can be used as an indirect selection criteria for weevil resistance.

Physico-chemical characteristics of rice (Oryza Sativa L.) grain imparting resistance and their association with development of rice weevil, Sitophilus oryzae (L.) (Coleoptera:Curculionidae)

Association between rice grain characteristics and Sitophilus oryzae development were deciphered through laboratory experiments. Among the different physical characteristics evaluated, significant and negative correlation of 100 seed weight was observed with weevil emergence (r = − 0.53) and susceptibility index (r = − 0.51). Hence, 100 seed weight was found out to be important characteristics of grain. Similarly, hardness of the grain delayed weevil emergence (r = − 0.41) and reduced the grain weight loss (r = − 0.245). Biochemical characteristic of grain, like protein was found positively associated with weevil emergence (r = 0.741) and negatively associated with median developmental period (r = − 0.537). Amylose being an important component of grain had negative relation with weevil emergence (r = − 0.007); median development period (r = − 0.093). Among different varieties tested, Cross-12 was found to be moderately resistant compared to others. It was the only variety having long broad grain and recorded highest 100 seed weight indicating size of the substrate could hinder the development of weevils. The aim of the current study is to decipher the association of development of S. oryzae and physico-chemical characteristics of grain governing it.

Susceptibility of selected maize seed genotypes to Sitophilus zeamais (Coleoptera: Curculionidae)

Studies were carried out under laboratory conditions of 25 ± 2 °C and 70 ± 5% RH in an incubator to determine the relative susceptibility of eighteen maize genotypes to attack by the maize weevil, Sitophilus zeamais Motschulsky. The experiment was laid out in a Completely Randomized Design (CRD) with three replications. Adult mortality, number of F1 progeny, weevil development time, susceptibility index, percentage seed damage, percentage weight loss, and weight of powder produced were determined after storage period of three months. The susceptibility index was determined using Dobie’s formula and the genotypes were classified into different susceptibility groups. The genotypes exhibited varying degrees of susceptibility to S. zeamais attack. Only Aseda was regarded as resistant and TZE-Y POP STR as moderately resistant to S. zeamais. Kpari-Faako, Tintim, WACCI-M-1215, WACCI-M-1594 and Wang-Dataa were regarded as moderately susceptible to S. zeamais. However, Abontem, Bihilifa, Ewul-Boyu, Sanzal-Sima, TZE-I 17, WACCI-M-1205, WACCI-M-1508 and WACCI-M-1510 were regarded as susceptible genotypes. Furthermore, Aburohemaa, Obaatanpa and Omankwa were regarded as highly susceptible to S. zeamais. Number of F1 progeny, seed damage, seed weight loss, weight of dust produced and seed moisture content had positive relationship with varietal susceptibility while adult weevil mortality, median development period and seed germination after infestation had an inverse relationship with susceptibility in maize. The use of insect resistant genotypes would offer a sustainable way of minimizing postharvest losses of seeds in storage especially for smallholder farmers who keep harvested grains for future use as food and seed.

English

The bruchid, Callosobruchus maculatus (F.) is one of the most destructive pests and causes substantial losses to cowpea during storage in tropical and subtropical regions. The development of successful breeding strategy requires knowledge on gene action and trait inheritance in local and improved sources. In this study, the mode of inheritance, the types of gene action and maternal effects of cowpea resistance to bruchid was investigated. Nine parental lines and their 72 F2 segregating populations, created in a full diallel Griffing’s method 1 approach, were evaluated for resistance to bruchid attack in a randomized complete block design (RCBD) with three replications. Data were recorded on number of eggs laid by the bruchid (NE), adult bruchid emergence (NEI), median development period (MDP) and Dobie Susceptibility index (DSI) was computed. Genotype had highly significant effects on NE, NEI and MDP and DSI. General combining ability (GCA) effects of parents, specific combining ability (SCA) effects of crosses, and maternal and reciprocal effects were highly significant for all the traits. The ratios of GCA to SCA for all the traits were greater than 50% suggesting the preponderance of additive over non-additive gene action in the expression of the traits. Narrow sense heritability estimates were 64.12, 77.69 and 80.99% for NE, NEI and MDP, respectively. Parents 2419, TVu-2027 and IT84s-2246 were identified as promising general combiners for resistance to bruchid and the seven best selected crosses based on their SCA and DSI values were, IT84s-2246 × 2419, 2419 × MU9, TVu-2027 × SECOW2W and 2419 × IT90K-76, 2419 × WC69, 2419 × SECOW5T and 2419 × SECOW2W. The selected parents and/or crosses could be valuable genetic materials for breeding cowpea resistance to bruchid in Uganda or similar environments. Key words: Additive gene action, heritability, median development period, reciprocal effects.

Resistance of Uganda soybean germplasm to Adzuki bean bruchid

Soybean (Glycine max (L.) Merrill) is among the major food and industrial crops grown globally for its high protein and oil content. Lately, in Uganda, soybean reportedly faces challenges with a storage pest, Callosobruchus chinensis. This study was carried out to quantify the damage caused by the pest and identify the sources of resistance in the germplasm in Uganda. The study was conducted at Makerere University Agricultural Research Institute, Kabanyolo (MUARIK) in Uganda, during 2015 and 2016. Callosobruchus chinensis was used to challenge 498 soybean lines under no choice condition, in the laboratory. Results showed no significant differences in eggs laid amongst the different genotypes; however the genotypes performed significantly different (P< 0.05) for adult insect emergence, median development period (MDP), Dobie susceptibility index (DSI), growth index (GI), insect percent emergence (% IE) and seed weight loss (%WL). Genotype AVRDC G8527 had the lowest % IE (6.31), DSI (0.7), % WL (0.02) and GI (0.07), suggesting high resistance. Weight loss of up to 27% was recorded in genotype USA 7. There was a strong positive correlation between number of adults that emerged with DSI (r=0.87), eggs (r=0.88), % weight loss (r=0.73), and growth index (r=0.996). Cluster analysis revealed that AVRDC G8527, a resistant genotype was closely related to S-line 13.2A, a moderate resistant genotype. Regression analysis, revealed that adult bruchid emergence explain seed weight loss with 62% coefficient of determination; while seed colour could be used to determine genotype DSI with up to 74% coefficient of determination. Genotypes AVRDC G8527 and G89 were identified as the most resistant genotypes based on levels of DSI. Keywords : Callosobruchus chinensis, Dobie susceptibility index, seed weight loss

Resistance of selected Mozambican local and improved maize genotypes to maize weevil, Sitophilus zeamais (Motschulsky)

Maize weevil Sitophilus zeamais (Motschulsky) is one of the most important pests of on-farm stored maize in thetropics, particularly where there is no control of moisture content and application of pesticides. This study aimed todetermine the level of resistance among Mozambican maize genotypes against S. zeamais. A total of 17 genotypes,composed of seven experimental hybrids developed from S5 inbred lines from five populations, one released hybrid,two improved open pollinated varieties (OPV), three landraces from Mozambique, two resistant and two susceptiblechecks from Kenya were screened for their resistance to S. zeamais. Four hybrids were screened at their F1 and F2generations. The genotypes were evaluated in the post-harvest laboratory, Kiboko, Kenya in a completely randomizeddesign, replicated 4 times. Data was collected on the number of emerged insects, seed weight loss, seed damage,median development period; and protein, starch and oil contents. The Dobie index of susceptibility was used to groupthe genotypes. Six of the of the eight hybrids at the F1 generation were resistant while two were moderately resistant.Three of the four hybrids evaluated at the F2 generation were moderately resistant while one was susceptible. Two ofthe five OPVs evaluated (EV8430DMRSR and landrace Kandjerendjere) were resistant. Genotypes with high proteincontent showed resistance while those with high starch contents showed susceptibility. Weevils fed on the resistantgenotype produced low number of F1 progeny, had a high median developmental time, caused low seed damage andlow seed weight loss. The resistant genotypes can be either used as cultivars or as sources of resistance in a breedingprogram for weevil resistance.

Genotypic variation for maize weevil resistance in eastern and southern Africa maize inbred lines

The maize weevil ( Sitophilus zeamais Motschulsky) is the most destructive storage insect pest of maize ( Zea mays L.) worldwide, especially among susceptible varieties. Breeding for grain resistance against the weevil is a major component of an integrated pest management strategy in maize production. The objective of this study was to identify diverse sources of weevil resistance for introgression in breeding programmes. A total of 180 inbred lines from three geographical areas were screened for maize weevil resistance. Screening was executed by infesting 50 g of maize grain with 32 newly emerged adult weevils, placed in 250 cm 3 glass jars in a “no-choice” laboratory test. The grain susceptibility parameters used were F 1 weevil progeny emergence, percent grain damage, median development period, Dobie’s index of susceptibility, and parental weevil mortality. New sources of weevil resistance for maize breeding were identified. Eight inbred lines were consistently resistant and, therefore, selected as potential donors for weevil resistance in the maize improvement programmes. There was significant genetic variation, and high levels of heritability (89 – 96%) for weevil resistance that suggested high potential for germplasm improvement through selection. No significant association was observed between maize weevil resistance and grain yield, suggesting that breeding for maize weevil resistance can be achieved without compromising grain yield. Keywords: Sitophilus zeamais , weevil resistance, Zea mays

Resistance in sorghum to Sitophilus oryzae (L.) and its association with grain parameters

Sorghum is the fifth most important cereal and suffers heavy damage from rice weevil Sitophilus oryzae, reducing their quality and quantity. Studies were conducted to identify the association of grain characteristics and their relationship with resistance to the rice weevil. The paper discusses the associations between sorghum seed parameters, insect oviposition, development data and grain weight loss. The important grain characteristics, viz., 100 seed weight was significantly positively correlated with grain hardness (0.55**) and median development period (0.47**) and significantly negatively correlated with grain weight loss (- 0.43*). However, the grain hardness was significantly negatively correlated with oviposition (- 0.49**), adult emergence (- 0.75**) and grain weight loss (- 0.82**) and was significantly positively correlated with median development period (0.85**). The pest parameter, viz., oviposition was significantly positively correlated with adult emergence (0.43*) and grain weight loss (0.55**). Two principal components (PCs) were extracted explaining cumulative variation of 76.2 %. Seed weight, grain hardness, oviposition, adult emergence, median development period and grain weight loss were the reliable variables for characterization of resistance to S. oryzae. The sorghum lines EC 24, EC 22, PEC 8, PEC 7, EP 78, EP 57, AKR 354 were classified as resistant to S. oryzae and these could be used in future breeding program as resistant sources.

Laboratory Assessment of the Levels of Resistance in Some Bean Varieties Infested with Bean Weevils (Acanthoscelides obtectus and Zabrotes subfasciatus)

The main objective of the study was to assess levels of resistance of some selected bean (Phaseolus vulgaris L.) varieties to storage bruchids (Common bean weevil Acanthoscelides obtectus (Say) and Mexican weevil Zabrotes subfasciatus ). Specifically it aimed at determining bruchids emergence and median development period, finding out the extent of damage caused by the bruchids on each variety and determining the weight loss incurred by each variety due to bruchids infestation. The experiment was laid out in a Complete Randomized Design (CRD) with four replicates. The study was conducted at Bunda college of Agriculture-Department of Crop and Soil Sciences-Entomology Laboratory. It was conducted from September 2012 to January 2013. Seven bean varieties, Kalima, Nasaka, BCB3, Sapelekedwa, BCB1, Bwenzilaana, and BCB2 were used as test materials. 100 g of bean seeds sample from each variety were put in kilner jars and were infested with 16 bruchids of common weevil and Mexican weevil, and it was carried in two phase; the first phase was used collect data for emerging insects and median development period;

Evaluation of open pollinated varieties of maize for resistance to the maize weevil in a controlled temperature and humidity laboratory in Zimbabwe

Maize weevil (Sitophilus zeamais Motschulsky) is one of the major maize storage pests among smallholder farmers in eastern and southern Africa (ESA), thereby, reducing total on-farm maize harvests. Experiments were conducted in a controlled temperature and humidity (CTH) laboratory at CIMMYT-Zimbabwe to compare the resistance of new maize open pollinated varieties (OPVs) from regional trials undertaken in ESA to maize weevils. Twenty maize OPVs were shelled and cleaned before being placed in a deep freezer at −20 °C to kill any pests and eggs in the grain from the field. Fifty grams of grain from each OPV was measured after 3 weeks and placed in the CTH lab for conditioning. The samples were placed in 250-mL jars with brass-screened lids and then infested with 32 maize weevils aged between 10 and 14 days. Data were collected for kernel hardness prior to weevil infestation, as kernel hardness to confer resistance to weevils. The components of maize weevil resistance considered were: median development period, Dobie index of susceptibility, weevil emergence, weevil mortality, weevil fecundity, grain weight loss, kernel damage and germination. There were highly significant differences in maize kernel characteristics and median development period (P < 0.001) among the maize OPVs. There were significant differences in the number of damaged kernels, grain weight loss (P < 0.01), weevil mortality and germination (P < 0.05) among the maize OPVs. There were no significant differences found for weevil progeny emergence (F1), Dobie index of susceptibility and weevil fecundity, the last of which was positively and significantly correlated with kernel damage (P < 0.001). The DIS was positively and significantly correlated with weight loss and F1 (P < 0.001). The maize OPVs 07WEEVIL, Chitedze6, Strigoff126, Strigoff128 and ZM625 were found to be resistant; on the other hand, Strigoff140, Strigoff125, Strigoff133, VP05199 and VP074 varieties were highly susceptible.

Comparative resistance of improved maize genotypes and landraces to maize weevil

A comparative study of maize (Zea mays L.) weevil (Sitophilus zeamais Motsch.) resistance in selected landraces and improved genotypes of maize, was conducted through a field experiment and laboratory assays. The maize grain characteristics that confer resistance to the maize weevil, Sitophilus zeamais Motschulsky, namely; grain hardness, weight and protein content, were compared in 50 improved maize genotypes developed by CIMMYT and two landraces (Cimambwe and Pandawe). The relative susceptibility of all maize experimental material to the weevil, were also compared using Dobie’s susceptibility indices, grain weight loss and median development period. Genotypes were significantly different (p 0.05) in the Dobie’s indices of susceptibility but exhibited a wide index range (0.77 to 9.11). The landrace, Chimambwe, had the second highest Median Development Period, while Pandawe, had the heaviest kernels, though without noticeable advantage in resistance to the weevil. The Open Pollinated Varieties (OPVs) were not superior to hybrids according to the Dobie’s index of susceptibility. The possibility of developing maize hybrids or OPVs that are as resistant to the maize weevil, S. zeamais, as or even better than landraces is discussed and recommendations made.

Traditional farmers’ knowledge of sorghum (sorghum bicolor [Poaceae]) landrace storability in Ethiopia

Traditional knowledge of grain storage was studied on small farms in Ethiopia. Sixteen of sixty landraces of sorghum collected from small farms in Shewa and Welo regions of Ethiopia were identified by the farmers as being stored sorghum landraces. Farmers were interviewed and asked to rate the storability of these stored-sorghum landraces with respect to the major insect pest of the area, the rice weevil. A farmers’ index of storability was then calculated for each landrace. The landraces were then assessed for rice weevil, Sitophilus oryzae (L.), susceptibility in standardized tests at 70% relative humidity and 27°C. The mean farmers’ index for the 16 landraces was found to be inversely related with the susceptibility parameters of F1 emergence (r2=0.80), oviposition (r2=0.76), weight loss (r2=0.88), and Dobie Index (r2=0.95). It was much less strongly related with the median development period (r2=0.20). The results show that farmer knowledge is an excellent guide to sorghum susceptibility to storage pests.

Comparison of improved and local maize varieties in the Republic of Benin with emphasis on susceptibility to Sitophilus zeamais Motschulsky

Experiments were conducted to verify differences in agronomic traits and susceptibility to the maize weevil, Sitophilus zeamais, in the field and in traditional maize storage systems between two international improved varieties, which have not been readily accepted by farmers in the Republic of Benin, one partially improved local variety and a local variety obtained from farmers. Factors responsible for differences in susceptibility and suitable screening methods for resistance to the maize weevil were also studied. In the first part of this study the varieties were compared in the field, during field drying and when stored using traditional techniques. The international improved varieties had significantly higher grain yield (60%) but had significantly poorer husk cover. The percentage of damaged ears following field drying, and the numbers of storage pests and grain weight loss after one month of storage were significantly higher in the international improved varieties presumably as a result of poorer husk cover. In the second part of this study the varieties were compared in a factorial arrangement of three storage forms (undehusked, dehusked and shelled grain) and two infestation methods (free and no-choice). Due to their superior husk cover quality, Benin varieties were significantly more resistant to weevils when infested in the traditional, undehusked storage form than international improved varieties. The smaller-grain, flinty, Benin varieties showed a significantly smaller number of F 1 generation weevils. A significant lengthening of the median development period (MDP) of weevils was observed when maize was stored as dehusked ears compared to shelled grain, particularly on the international improved varieties. No improved vs Benin variety comparisons interacted with free vs no-choice comparisons except for index of susceptibility in the undehusked storage form. Free choice infestations resulted in increased experimental error for number of F 1 weevils, presumably due to a clumped distribution of female weevils during oviposition. When the target farmer's storage system is undehusked ears, it is suggested to use no-choice infestation of undehusked ears as a screening method for elite candidate varieties. An assessment of husk quality and no-choice infestation of shelled grain and/or dehusked maize ears is suggested as more appropriate for preliminary screening of diverse germplasm.

Effects of shelling maize cobs on the oviposition and development of Sitophilus zeamais Motschulsky

Oviposition and development of Sitophilus zeamais Motschulsky were studied on shelled maize kernels and unshelled cobs of the variety “Blanc Deux Precoce” from the Republic of Benin. On unshelled cobs adult weevils must feed and oviposit mostly on the kernel's crown, the only part of the kernel fully exposed to the external environment. The resistance of unshelled kernels to the maize weevil, relative to shelled kernels, is shown to depend on three factors: (1) reduced oviposition, as a result of non-preference for oviposition on the kernel's crown; (2) an increase in weevil median development period (MDP) due to the less suitable endosperm diet of first instar larvae which hatch from eggs laid on or near the crown; and (3) an additional increase in MDP due to difficulty in finding a site on the kernel where the F 1 generation adult can emerge. These resistance factors, which contribute to lower levels of weevil infestation in traditional on-the-cob maize storage, have not been thoroughly investigated before. Other kernel and cob characteristics which appear to contribute to resistance are also discussed.