Resistance in sorghum to the shoot fly, Atherigona soccata: epicuticular wax and wetness of the central whorl leaf of young seedlings

Sorghum genotypes known to be resistant or susceptible to shoot fly, Atherigona soccata Rondani were examined by scanning electron microscopy for differences in epicuticular wax structure and wetness of the central leaf whorl. Two major types of wax structures were observed: shoot fly resistant and moderately resistant genotypes were characterised by a smooth amorphous wax layer and sparse wax crystals while susceptible genotypes possessed a dense meshwork of crystalline epicuticular wax. The density of wax crystals decreased from the third leaf to the seventh leaf stage and was related to both seedling age and leaf position. Water droplets on susceptible genotypes with dense wax crystals showed spreading at the edges indicating a tendency to wet easily. In resistant genotypes with less dense wax crystals the droplets remained intact and did not spread.     

Morphological factors of the central whorl leaf associated with leaf surface wetness and resistance in sorghum to shoot fly,Atherigona soccata*

Earlier studies showed that leaf surface water on the central whorl leaf of sorghum seedlings is associated with resistance to shoot fly. In this study, the results of an experiment to determine if leaf surface wetness (LSW) originates from atmospheric condensation or from the plant are described. Morphological structures: trichomes, stomata, leaf cuticle and quantity of surface wax of the central whorl leaf were also examined for their role in LSW production. The results suggest that LSW of the central whorl leaf originates from the plant and is not due to condensation of atmospheric moisture. The presence of trichomes was indirectly associated with LSW and resistance to shoot fly but stomatal density was not associated with LSW production. The amount of wax extracted per 100 mg of fresh weight varied significantly between genotypes and seedling age. It was more in susceptible than in resistant genotypes; however, cuticular thickness was not associated with resistance. It is suggested that LSW could be the result of some form of cuticular movement of water to the leaf surface.     

Genomic diversity among sorghum genotypes with resistance to sorghum shoot fly, Atherigona soccata

Host plant resistance is one of the important components for management of sorghum shoot fly, Atherigona soccata. The levels of resistance in cultivated germplasm are low to moderate, and therefore, it is important to identify sorghum genotypes with diverse mechanisms of resistance based on physico-chemical and or molecular markers. We assessed the genetic diversity of 15 sorghum genotypes with different levels of resistance/susceptibility to shoot fly, A. soccata using 93 sorghum simple sequence repeat (SSR) primer pairs and simultaneously characterized for 15 morpho-biochemical traits associated with shoot fly resistance. Of these 93 SSR primer pairs, amplification products from 79, thought to correspond to single-copy loci distributed across all ten sorghum chromosome pairs, showed good polymorphism across the 15 sorghum genotypes. The polymorphic information content (PIC) values of these 79 SSR markers ranged from 0.06 to 0.86. The Principal Coordinate Analyses (PCoA) and cluster analyses based on dissimilarity matrices derived from SSR based allelic variation (Neighbor-Joining distance) and variation in 15 morpho-biochemical traits (based on Gower??s distance), revealed grouping of most susceptible genotypes in single cluster. The improved breeding lines grouped with resistant or susceptible genotypes, based on shared pedigree. Based on these results, three resistant accessions viz., IS 1054, IS 1057 and IS 4664 were found diverse to IS 18551, which is widely used as shoot fly resistance donor. These diverse sources, after further characterization for resistance mechanisms, can be used in breeding programs for improving shoot fly resistance.     

Leaf surface wetness in sorghum and resistance to shoot fly, Atherigona soccata: role of soil and plant water potentials

In experiments with potted plants, the relationships between soil matric potential, plant water potential and production of water droplets (leaf surface wetness) on the folded central whorl leaf of seedlings of sorghum genotypes that are either resistant or susceptible to shoot fly (Atherigona soccata) damage were investigated. Differences in soil matric potentials in the pots affected the plant water status, which in turn had profound effects on the production of water droplets on the central whorl leaf of the sorghum genotype susceptible to shoot fly. There was no consistent variation in the relationship between plant water potential and soil matric potential of resistant and susceptible sorghum genotypes. However, there was very little or practically no water droplets on the central whorl leaf of the resistant genotypes, indicating that the production of water droplets is not solely the result of internal water status of the plant. It is suggested that leaf surface wetness is genetically controlled and that an understanding of the mechanism by which water is transferred to the leaf surface will enhance breeding for resistance to shoot fly.     

Effect of planting dates and maize hybrids on the infestation with sorghum shootfly,Atherigona soccata Rondani and its effect on the yield

Abstract

Twenty maize hybrids plus local were tested for their susceptibility to major pests of sorghum shootfly, Atherigona soccata Rondani under field conditions at Sohag governorate during three planting dates (20th April, 20th May and 5th July) sown during two tested years (2004 and 2005 seasons). The investigation showed that when the sowing dates were considered irrespective of the different years or the maize hybrids it was evident that during the first planting date (20th April), the maize hybrids harboured the highest levels of infestation with sorghum shootfly, Atherigona soccata Rondani. The second planting date (20th May) was the least affected while the third planting date (5th July) received moderate levels of infestation. Results also showed that the average infestation of Atherigona soccata during both seasons was a significantly negative correlation affected by the sowing dates and maize hybrids. The yield of maize hybrids negatively correlated with percentage of infestation by Atherigona soccata. The highest yield obtained from the maize hybrids was slightly infested by Atherigona soccata and sown during the planting date of 20th May. Therefore, the second sowing date (20th May) may be recommended as a proper cultivating date for maize hybrids as it brought about reduction not only in infestation but was also a good method to reduce chemical control. Our results indicated that none of the maize hybrids evaluated were found to be resistant to Atherigona soccata attack but maize hybrids were significantly different in their susceptibility and less than of a local control to the infestation with Atherigona soccata and divided into four groups, the first one was highly susceptible including Giza Baladi; the second group was susceptible including ten maize hybrids namely, Hf 155, Bionear 3062, Bionear 30k8, Nagah 18, Watania 4, HC 326, HC 327, Nafratity, Watania 1 and Bionear; the third group was low resistance including six maize hybrids namely, Hf 122, Hf 123, Hf 129, Hc314, Hc 325 and Hc 352; while the fourth group included Hf 10, Hf 124, Hc 311and Hc 324 and moderately resisted the Atherigona soccata infestation. These may serve as a good material for growing in the areas where the pest is a problem.     

Leaf surface chemistry of sorghum seedlings influencing expression of resistance to sorghum shoot fly, Atherigona soccata

Sorghum shoot fly, Atherigona soccata is one of the serious constraints to sorghum production, and host plant resistance is an important component for controlling this pest. We studied the expression of resistance to A. soccata in a diverse array of sorghum genotypes in relation to composition of leaf surface chemicals during the seedling stage. The sorghum genotypes IS 1054, IS 1057, IS 2146, IS 4664, IS 2312, IS 2205, SFCR 125, SFCR 151, ICSV 700, and IS 18551 exhibited antixenosis for oviposition, and suffered less deadhearts due to sorghum shoot fly, A. soccata. Compounds undecane 5- methyl, decane 4- methyl, hexane 2, 4- methyl, pentadecane 8- hexyl, and dodecane 2, 6, 11- trimethyl, present on the leaf surface of sorghum seedlings, were associated with susceptibility to shoot fly; while 4, 4- dimethyl cyclooctene was associated with resistance to shoot fly. The compounds associated with resistance/susceptibility to shoot fly, can be used as marker traits to select for resistance as well as for diversifying and increasing the levels of resistance to this pest. The role of biochemical compounds for developing sorghum varieties with resistance to shoot fly, A. soccata has been discussed.     

Biology ofTrichogrammatoidea simmondsi (Hym.: Trichogrammatidae) on sorghum shoot fly,Atherigona soccata (Dipt.: Muscidae) eggs

Experiments were conducted in a rearing room to study the biology ofTrichogrammatoidea simmondsi Nagaraja (Hym.: Trichogrammatidae) on sorghum shoot fly,Atherigona soccata Rondani (Dipt.: Muscidae) eggs. Shoot fly eggs were divided in two groups: 1) eggs < 24 h old and, 2) > 24 h old eggs. Thirty eggs of each group were used in a randomized complete block design with four replicates. Shoot fly eggs less than 24 h old were preferred (73% of parasitism) over 24 h old eggs (7.25%). Three larval instars ofT. simmondsi were observed. Few eggs with twoT. simmondsi exit holes (1.87%) were recorded in > 24 h old eggs compared with < 24 h ones (3.74%). The sex ratio male: female was 1 ∶ 1.47. The development from oviposition to adult emergence ranged from 7 to 12 days (average=9.8±1.31, n=40), and the average life span of male and femaleT. simmondsi was 25±1.46 h (range 22–26 h, n=12) and 35.17±10.9 (range 25–50 h, n=28) respectively at 26° C, 60–65% R.H. and 12 ∶ 12 (L/D) photoperiod. This paper constitutes the first published information on the biology ofT. simmondsi on the sorghum shoot fly eggs.

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Résumé Des essais ont été conduits en salle d'élevage en vue d'étudier la biologie deTrichogrammatoidea simmondsi Nagaraja (Hym.: Trichogrammatidae) sur les œufs de la mouche des pousses du sorgho,Atherigoa soccata Rondani (Dipt.: Muscidae). Les œufs de la mouche ont été divisés en deux groupes: 1) ℧ufs agés de < 24 h, 2) > 24 h. Trente œufs de chaque groupe ont été utilisés dans un dispositif en blocs complets randomisés à quatre répétitions. Les œufs de moins de 24 h d'age ont été plus parasités (73% de parasitisme) que ceux de plus de 24 h d'age (7,25% de parasitisme). Trois stades larvaires deT. simmondsi ont été observés. La présence de deux trous d'émergence deT. simmondsi était moins élevée (1,87%) dans les œufs de > 24 h que dans ceux de < 24 h (3,74%). Le sex ratio male: femelle était de 1 ∶ 1,47 Le cycle de développement de l'œuf à l'émergence de l'adulte variait de 7 à 12 jours avec une moyenne de 9,8±1,31 (n=40). La durée moyenne de vie du male et de la femelle deT. simmondsi était respectivement de 25±1,46 h (variation 22–26 h, n=12) et 35,17±10,9 (variation 25–50 h, n=28) à 26°C, 60–65% H.R. et une photopériode de 12 ∶ 12. Cet article constitue la première information publiée sur la biologie deT. simmondsi sur les œufs de la mouche des pousses du sorgho.

     

Daily rhythms in the sorghum shootfly, Atherigona soccata: oviposition, egg-hatch and adult eclosion

ABSTRACT. Daily rhythms controlling oviposition, egg-hatching and adult eclosion in the sorghum shootfly, Atherigona soccata Rondani, were investigated. Eggs were laid only during the photophase of a LD 12:12 cycle, in two peaks. Under continuous light, this oviposition was considerably attenuated but not made immediately arrhythmic. Egg-hatching and adult eclosion both commenced just before dawn. Some feature of the scotophase during or immediately after black-head formation apparently acts as a signal for hatching. Eclosion was controlled by light but its timing in the field was modified by temperature. The last 2–3 days of the pupal period constituted the most sensitive stage, and light signals received during this period determined the time of eclosion. Ecological advantages of these rhythms to the shootfly are discussed.     

Resistance in sorghum to shoot fly Atherigona soccata: Evidence for the source of leaf surface wetness

Leaf surface wetness (LSW) of the central whorl leaf of sorghum seedlings has been associated with susceptibility to shoot fly. Previous physical and physiological evidence suggested that LSW originates from the plant. This was confirmed by radioactive labelling methods using tritium and carbon-14. Tritiated water applied to the soil of potted seedlings was translocated to the surface of the whorl leaf. There were significant differences in the amount of tritiated water collected from susceptible (CSH 5) and resistant (IS 18551) genotypes. Studies with carbon-14 labelling of sorghum seedlings indicated the presence of (small amounts of) solutes in the surface water that may affect larval movement and survival.     

Reduction of shoot fly damage in irrigated post-rainy season sorghum by manipulating irrigation

Soil moisture was manipulated in an attempt to control shoot fly (Atherigona soccata Rondani) incidence in irrigated post-rainy season sorghum grown under a rainout shelter (ROS) and in field conditions. After uniform irrigation at sowing, the plants were subjected to water stress at young seedling stage (7–28 days after emergence, DAE) for different lengths of time. Soil water had profound effects on the production of water droplets on the surface of the central whorl leaf of seedlings (leaf surface wetness, LSW) of sorghum genotypes. LSW, which facilitates movement of the larvae, was more drastically affected in susceptible (CSH 5) than in moderately resistant (IS 1054) sorghum genotypes. Shoot fly oviposition (infestation) and deadhearts (crop damage) were much higher in treatments with full irrigation (control) than in treatments to which less water was applied during the first 3 wk after seedling emergence. This resulted in higher plant biomass and overall grain yield in the latter treatments than in the control. Using insecticides to control shoot fly infestation, it was shown that a simple cultural practice of inducing plant stress by reduced soil moisture content during early plant growth gave the same or better control of shoot fly damage and the same or higher grain yield than insecticide-protected plots with full irrigation. Thus the costs associated with irrigation requirement and insecticide can be greatly reduced in the former management option compared with the latter. It is suggested that manipulation of soil water content during the vulnerable early stages of crop growth can reduce shoot fly damage in irrigated post-rainy season sorghum.     

Natural Enemies of Sorghum Shoot Fly, Atherigona soccata Rondani (Diptera: Muscidae)

The sorghum shoot fly, Atherigona soccata is one of the most important pests of grain sorghum in Asia, Africa and the Mediterranean Europe. This paper reviews the current state of information on diversity, ecobiology, parasitism levels, and mass rearing of the parasitoids, predators and pathogens attacking different stages of A. soccata . Among the parasitoids, Trichogramma chilonis Ishii and Trichogrammatoidea simmondsi Nagaraja on the eggs, and Neotrichoporoides nyemitawus Rohwer on the larvae are most important. Although 15 species of predators have been recorded, their predation potential has not been assessed under field conditions. Several species of spiders are important predators on eggs. The ecobiology of T. chilonis, T. simmondsi, N. nyemitawus, Spalangia endius Walker and Trichopria sp. has been studied in considerable detail. The parasitism levels are quite high during the post-rainy season by Aprostocetus sp., N. nyemitawus , Opius sp. and S. endius . Augmenting populations of T. chilonis does not reduce the shoot fly infestation under field conditions. Parasitism by N. nyemitawus is greater in sorghum-cowpea intercrop than where sorghum is the sole crop. Mass rearing techniques are available only for T. chilonis and T. bactrae . The constraints and challenges for utilizing the natural enemies in integrated pest management have been discussed.     

The dynamics of leaf surface wetness of sorghum seedlings in relation to resistance to the shoot fly, Atherigona soccata

In quantitative measurements of leaf surface wetness (LSW) of the central whorl leaf of sorghum seedlings in August (rainy season) and November (post-rainy season), the highest amount (6.29 mg of water) was recorded in August in the shoot fly Atherigona soccata (Diptera: Muscidae), susceptible sorghum genotype CSH 1, while the lowest (0.07 mg) was recorded in November in the resistant genotype IS 18551. Studies on diurnal fluctuation revealed that LSW was lowest at sunset, was highest between 02.00 and 04.00 h (closely corresponding with hatching of shoot fly eggs) and dropped before sunrise. This fluctuation was associated with the evaporation of water from the plant during the night. More LSW accumulation occurred during the main crop season (June-October) than in the post-rainy season (November-April). Annual fluctuation of LSW followed trends similar to the population dynamics of shoot fly and crop infestation and were correlated with rainfall, temperature and relative humidity. Measurements of leaf temperature and the vapour pressure gradient between the leaf and the air indicated that leaf surface water originates from the plant. This was further supported by the different amounts of LSW on susceptible and resistant cultivars with similar microclimatic conditions.     

Observations on longevity and fecundity of the sorghum shoot fly, Atherigona soccata (Diptera; Anthomyiidae)

Longevity and fecundity of the sorghum shoot fly, Atherigona soccata Rond. were mainly affected by the adult food. Lack of mating reduced fecundity and affected the rate of oviposition in the females, but did not affect longevity. The mean number of eggs per mated female was 62.8±0.9. Oviposition began at a mean period of 4.7 days after adult emergence. Mean longevity of females and males was 32.6±0.3 and 25.4±0.4, days, respectively.

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Résumé La longévité et la fécondité de Atherigona soccata dépendent avant tout de la nourriture de l'adulte. L'absence d'accouplement réduit la fécondité et modifie le taux de ponte des femelles, mais ne touche pas leur longévité. Le nombre moyen d'ufs pondus par femelle accouplée est 62,8±0,9 (extrêmes 10–167). La ponte commence en moyenne 4–7 jours après l'émergence des adultes (extrêmes 2 et 14 jours). La longévité moyenne des femelles et des mâles est respectivement de 32,6±0,3 jours et 25,4±0,4 jours.

     

Ovipositional behaviour and host-plant preference of the sorghum shoot fly, Atherigona soccata (Diptera; Anthomyiidae)

The distribution of eggs on sorghum by Atherigona soccata Rond. and host preference for oviposition were studied. The female laid her eggs more or less evenly on sorghum leaves, laying one or two eggs per leaf. Under field conditions eggs were most frequently laid on the third leaf, followed by the second leaf, while under insectary conditions the second leaf was preferred to the third. Sorghum bicolor was markedly preferred to other graminaceous plant species, Digitaria scallarum, Rottboellia exaltata, Setaria verticillata and Panicum maximum.

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Résumé Nos observations montrent que les femelles d'Atherigona soccata répartissent leurs ufs plus ou moins au hasard sur les feuilles de Sorgho, déposant 1 à 2 ufs par feuille. Dans les conditions naturelles les ufs sont plus fréquemment déposés d'abord sur la 3ème feuille, puis sur la 2ème feuille, tandis qu'en insectarium la 2ème feuille est préférée à 3ème. Sorghum bicolor est nettement préféré à d'autres espèces de graminées, comme Digitaria scallarum, Rottboellia exaltata, Setaria verticillata et Panicum maximum.

     

When the going gets tough: Responses of Sorghum bicolor L. (cv. Tegemeo) seedlings to soil penetration resistance

Summary

Sorghum bicolor L. (cv. Tegemeo) seedlings were grown for nine days in soil at field capacity packed to give a uniform penetration resistance (PR) of either 0.25, 1.00 or 1.75 MPa. Root biomass was not significantly affected by soil PR treatment. However, as PR increased to 1.75 MPa, the diameter of the seminal root axis increased by 52% whilst its length decreased by 30%. Shoot growth, in terms of oven dry (OD) weight and photo-synthetic area, was reduced in both the 0.25 MPa and 1.75 MPa treatments compared to the 1.00 MPa treatment. A reduced nutrient, water or oxygen supply to the roots were discounted as possible causes of the root and shoot responses to soil PR. It is suggested that the changes in root morphology between treatments were a direct result of the changes in soil PR. For shoot growth, in the 0.25 MPa treatment it is suggested that shoot growth was reduced as a result of an increase in the carbon sink strength of the roots.     

The role of leaf surface wetness in larval behaviour of the sorghum shoot fly, Atherigona soccata

The susceptibility of sorghum to the shoot fly Atherigona soccata Rondani, (Diptera: Muscidae) is affected by seedling age and is highest when seedlings are 8–12 days old. This corresponds with high moisture accumulation on the central leaf which is the path of newly hatched larva as it moves downwards from the oviposition site, towards the growing apex. Studies showed that leaf surface wetness (LSW) of the central shoot leaf was higher in 10-day old seedlings than in seedlings of other ages. Similarly, LSW was much higher in the susceptible sorghum genotype CSH 1 than in the resistant genotype IS 2146. Larvae moved faster towards the growing point and produced deadhearts much earlier in CSH 1 than in IS 2146. They also moved faster in 10-day old seedlings than in seedlings of other ages. It was also shown that the leaf surface wetness of the central shoot leaf is a more reliable parameter of resistance than the glossy leaf trait or trichome density.

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L'influence de la humidité de la surface foliaire sur le comportement de la mouche des pousses du sorgho

Résumé La sensibilité du sorgho à la mouche des pousses du sorgho, Atherigona soccata Rondani, est liée à l'âge de la plantule. Elle est plus forte lorsque la plantule est âgée de 8 à 12 jours et la sensibilité est maximale à 10 jours. A ce stade de croissance on observe une forte accumulation d'humidité sur la feuille centrale de la tige. Les jeunes larves traversent cette zone humide lorsqu'elles descendent vers la zone de croissance à partir des pontes déposées sur la face ventrale des feuilles déroulées.Des études ont été menées à l'ICRISAT (Inde) sur la relation entre l'humidité de la feuille centrale de la tige des plantules du sorgho et les dégâts provoqués par la mouche des pousses. L'humidité de la surface des feuilles (HSF) a été estimée grâce à une échelle visuelle graduée 1 à 5 où, 1 = pas d'humidité apparente et 5 = surface de la feuille recouverte de gouttes d'eau. La HSF est plus élevée sur des pousses de sorgho âgées de 10 j que sur les pousses appartenant à d'autres classes d'âge. Les valeurs observées sont également plus fortes pour les variétés non résistantes à ce ravageur (CSH 1,4.8) que pour les variétés résistantes (IS 2146, (2)). La vitesse du déplacement larvaire entre le cornet et la zone de la croissance varie en fonction de l'âge de la plante et des cultivars. Les larves migrent plus rapidement vers la zone de croissance et provoquent la mort du coeur du sorgho plus tôt dans la variété CSH 1 que dans IS 2146. Les larves se déplacent plus rapidement dans les pousses âgées de 10 j que dans les pousses appartenant à d'autres classes d'âge.Des études ont également démontré que la HSF n'est pas directement liée au caractère feuille lisse où à la densité des trichomes. La HSF est faible pour les génotypes résistants présentent où non le caractère feuille lisse. Par contre la HSF est élevée pour les génotypes non résistants présentant le caractère feuille lisse ou non. Aucune relation directe entre la densité des trichomes et les dégâts provoqués par la mouche des pousses n'a pu être mise en évidence. L'analyse des correlations établie pour les caractères de surface des feuilles avec la mort du cur des sorghos indique que les correlations sont faibles et non-significatives pour le caractère feuille lisse (0.49) et la densité des trichomes (0.39 et 0.2). Par contre les correlations sont fortes et significatives pour la HSF (0.82).On conclue que la HSF de la feuille centrale de la tige est un facteur important dans le déterminisme de la résistance du sorgho vis à vis de la mouche des pousses. Les relations entre les processus physiologiques de la plante et les facteurs impliquées dans l'accumulation d'eau sur la surface des feuilles font actuellement l'objet d'études détaillées.

     

Antixenosis component of resistance to sorghum midge, Contarinia sorghicola Coq. in Sorghum bicolor (L.) Moench

Sorghum midge, Contarinia sorghicola Coq. (Diptera: Cecidomyiidae) is the most destructive pest of grain sorghum, and host-plant resistance is an effective method of controlling this insect. We studied the antixenosis component of resistance to sorghum midge using multi-, double- and no-choice cage tests, and under multi-choice field conditions to quantify and understand the nature of antixenosis component of resistance to this insect in Sorghum bicolor (L.) Moench. Midge response towards sorghum panicles was influenced by panicle size and cage type used to study the orientation behaviour. Maximum number of midges were recorded at 30 and 60 min after initiating the experiment. Antixenosis shown by C. sorghicola under multi-choice field conditions to ICSV 197 and TAM 2566 was not confirmed under cage tests, while DJ 6514, AF 28 and IS 3461 were non-preferred both under field and cage conditions. Midge-resistant female parents (PM 7061 and PM 7068) were less preferred than the midge susceptible (ICSA 42 and 296A) female parents. Male-sterility did not influence host finding and acceptance by the midge females, although in one out of two tests, the maintainer lines (B-lines) were preferred over the male-sterile lines (A-lines).     

Molecular mapping of the rf1 gene for pollen fertility restoration in sorghum (Sorghum bicolor L.)

We report the molecular mapping of a gene for pollen fertility in A1 (milo) type cytoplasm of sorghum using AFLP and SSR marker analysis. DNA from an F₂ population comprised of 84 individuals was screened with AFLP genetic markers to detect polymorphic DNAs linked to fertility restoration. Fifteen AFLP markers were linked to fertility restoration from the initial screening with 49 unique AFLP primer combinations (+3/+3 selective bases). As many of these AFLP markers had been previously mapped to a high-density genetic map of sorghum, the target gene (rf1) could be mapped to linkage group H. Confirmation of the map location of rf1 was obtained by demonstrating that additional linkage group-H markers (SSR, STS, AFLP) were linked to fertility restoration. The closest marker, AFLP Xtxa2582, mapped within 2.4 cM of the target loci while two SSRs, Xtxp18 and Xtxp250, flanked the rf1 locus at 12 cM and 10.8 cM, respectively. The availability of molecular markers will facilitate the selection of pollen fertility restoration in sorghum inbred-line development and provide the foundation for map-based gene isolation. Received: 22 August 2000 / Accepted: 18 October 2000     

Components of resistance to the sorghum midge, Contarinia sorghicola

Studies were conducted on components of resistance to sorghum midge on four resistant (DJ 6514, AF 28, TAM 2566 and IS 15107) and two susceptible cultivars (CSH 1 and Swarna). Data were recorded on the numbers of eggs, larvae, emerged adults and grain damage in panicles of different genotypes infested with 60 midge females/panicle under no-choice conditions. The size of floral parts (glume, lemma, palea, lodicule, stigma, style, ovary and anther), rate of grain development and tannin content of grain were measured. The lengths of glume gl and 82, lemma L1 and L2, palea, lodicule, anther, style and stigma were positively associated with susceptibility to sorghum midge. Rate of grain development (between 3rd and 7th day after anthesis) was negatively associated with susceptibility to sorghum. Tannin content of grain was also negatively correlated with midge susceptibility, although there were distinct exceptions (e.g. DJ 6514 is highly resistant bur has a low tannin content).