Stenodiplosis Sorghicola Research Articles

Host‐plant preference and oviposition responses of the sorghum midge, Stenodiplosis sorghicola (Coquillett) (Dipt., Cecidomyiidae) towards wild relatives of sorghum

Sorghum midge, Stenodiplosis (Contarinia) sorghicola (Coquillett) is an important pest of grain sorghum world‐wide. Considerable progress has been made in screening and breeding for resistance to sorghum midge. However, some of the sources of resistance have become susceptible to sorghum midge in Kenya, in eastern Africa. Therefore, the wild relatives of Sorghum bicolor were studied as a possible source of new genes conferring resistance to sorghum midge. Midge females did not lay eggs in the spikelets of Sorghum amplum, Sorghum bulbosum, and Sorghum angustum compared to 30% spikelets with eggs in Sorghum halepense when infested with five midge females per panicle under no‐choice conditions. However, one egg was laid in S. amplum when infested with 50 midges per panicle. A larger number of midges were attracted to the odours from the panicles of S. halepense than to the panicles of Sorghum stipoideum, Sorghum brachypodum, S.angustum, Sorghum macrospermum, Sorghum nitidium, Sorghum laxiflorum, and S. amplum in dual‐choice olfactometer tests. The differences in midge response to the odours from S. halepense and Sorghum intrans were not significant. Under multi‐choice conditions, when the females were also allowed a contact with the host, more sorghum midge females were attracted to the panicles of S. bicolor compared with S. amplum, S. angustum, and S. halepense. In another test, numerically more midges responded to the panicles of IS 10712 compared with S. halepense, whereas the differences in midge response to the panicles of ICSV 197 (S. bicolor) and S. halepense were not apparent, indicating that S. halepense is as attractive to sorghum midge females as S. bicolor. The wild relatives of sorghum (except S. halepense) were not preferred for oviposition, and they were also less attractive to the sorghum midge females. Thus, wild relatives of sorghum can prove to be an alternative source of genes for resistance to sorghum midge.

Cytoplasmic male-sterility and source of pollen influence the expression of resistance to sorghum midge, Stenodiplosis sorghicola

Sorghum midge, Stenodiplosis (Contarinia) sorghicola (Coquillett), is an important pest of grain sorghum, and host plant resistance is an important aspect of control of this pest. This research investigated how cytoplasmic male-sterility and source of pollen influence the expression of resistance to sorghum midge. Sorghum midge emergence was significantly lower in panicles of midge-resistant and midge-susceptible cytoplasmic male-sterile lines when pollinated with AF 28 - a midge-resistant restorer line, than those pollinated with Swarna - a midge susceptible restorer line, indicating the presence of xenia effects. Maintainer lines (B-lines) of midge-resistant parents had significantly lower numbers of eggs and larvae than the B-lines of midge-susceptible parents. Male-sterile lines of the both midge-resistant and midge-susceptible lines were equally susceptible, indicating that resistance to sorghum midge is influenced by factors in the cytoplasm of the B-line. These findings will have an important bearing on the production of hybrids with resistance to insects.

Evaluation of planting date, sorghum hybrid, and insecticide treatment on sorghum midge (Diptera: Cecidomyiidae) management in northeast Louisiana.

The combined effect of planting date, insecticide treatment, and host-plant resistance was studied in northeast Louisiana for management of the sorghum midge, Stenodiplosis sorghicola (Coquillett), during 1994 and 1995. Significantly higher numbers of sorghum midges were observed visiting flowering spikelets of the midge-susceptible sorghum hybrid (Delta and Pine Land 'DP1552') than those of the midge-resistant sorghum hybrid (DeKalb 'DK-60'). Numbers of midges averaged 1.2 and 0.6 per flowering panicle in the susceptible and resistant sorghum hybrids, respectively, in 1994 and 1.8 and 1.0, respectively, in 1995. Midge densities increased significantly as the sorghum flowering season progressed. Sorghum midge reached peak densities during the first half of August in 1994 and 1995. The length of the flowering period in the early-planted (mid-March) sorghum was significantly longer compared with the flowering periods in the mid-April, mid-May, or mid-June planted sorghums. This resulted in prolonged exposure of flowering panicles to ovipositing midges and increased midge damage in the early-planted (mid-March) sorghum. Damage by sorghum midge was significantly higher in the early-planted (mid-March) sorghum hybrids than in the late-planted (mid-June) sorghum hybrids. The midge-susceptible hybrid produced highest yields when planted in mid-April and mid-May (optimum period) and lower yields when planted very early (i.e., mid-March) or late (i.e., mid-June). No significant differences were observed in yields for the resistant hybrid at any planting date in 1994. However, in 1995, significantly lower yields were recorded in resistant sorghum planted in mid-June. Levels of sorghum midge damage and sorghum seed yields in the untreated resistant hybrid were not significantly different than those observed in the insecticide-treated susceptible hybrid. Numbers of adult midges captured on sticky traps were positively correlated to numbers of visual estimates of ovipositing midge females visiting flowering spikelets.

Midge Resistance and Hydrocyanic Acid Content of Sorghum bicolor

Sorghum midge (Stenodiplosis sorghicola [Coquillett]) is found in most countries where sorghum (Sorghum bicolor L. Moench) is grown (Doggett 1988). A number of sorghum lines resistant to the sorghum midge have been identified (Teetes 1985). Various mechanisms have been proposed for midge resistance, including cleistogamy, nonpreference, antibiosis, tannin content, and glume size and tightness (Doggett 1988 and Teetes 1985). Dhurrin[p-hydroxy-(S)-mandelonitrile-$-D-glucoside] is the cyanogen of sorghum (Gorz et al. 1977) that is enzymatically hydrolyzed to cyanide and p-hydroxybenzaldehyde (p-HB) when cellular integrity is interrupted (Wajant et al. 1994). Gorz et al. (1977) reviewed studies that showed colorimetric methods can be used to determine cyanogen content or hydrocyanic acid potential (HCN-p) in plant tissue. In an unrelated study in search for cyclic hydroxamic acids (e.g., DIMBOA), the second author (M. D. Richardson) found that midge resistant sorghum genotypes, Huerin and Tift MR88, produced 0.52 and 0.78 mg p-HB while midge intermediate (genotype 1821 cm) and midge susceptible (Tx623B) genotypes produced 0.18 and 0.15 mg p-HB per g fresh weight [LSD(0.05) = 0.10], respectively (unpublished data). The objective of this study was to determine whether resistance to sorghum midge may be related to HCN levels. In this study, three replications (pots) of 10 genotypes (Table 1) of sorghum with varying levels of midge resistance were planted in 20 cm wide plastic pots in the greenhouse on 17 Nov 1993 in a randomized complete block design. Plants were thinned to six plants per pot at ten days after planting. Response of the genotypes to midge (Table 1) were determined in a previous unpublished study, where a rating of 0 = resistant and 9 = susceptible. These entries were part of a larger experiment arranged in a randomized complete block with four replications where genotypes were rated for midge resistance under natural midge infestation at Tifton, Georgia. All genotypes in this study were inbred lines except DeKalb E57, Hyperformer, AgraTech 712G and Pioneer 8333 which were F, hybrids. Plants were grown under uniform temperature (28 to 30E C) and moisture conditions in the greenhouse. Plants were fertilized with a complete water-soluble fertilizer to maintain healthy growth. HCN contents were analyzed by analysis of variance procedures (SAS Institute, Inc., 1985) to evaluate genotype effects. Differences between genotype means were separated by the least significance difference (LSD) test at the 0.05 probability level. Leaf discs from non-expanded leaves of the six plants (50 days old) in a pot were cut with a #3 cork cutter and placed in 10 ml test tubes. Leaf tissue from each genotype in each replication weighed 0.07 g. No significant differences in dry weights of the leaf tissue were observed among replications and genotypes. Four drops of chloroform were added to each test tube. We used the colorimetric technique and standards described by Hogg and Ahlgren (1942). HCN content of the solutions were determined using a Milton Roy Company Spectronic 501 at 540 nm with Mr. Sipper.

Identification of stable sources of resistance in sorghum to midge and their reaction to leaf diseases

Sorghum midge ( Stenodiplosis (= Contarinia) sorghicola Coquillett) is an important pest of grain sorghum worldwide, and several sources of resistance have been identified in the world sorghum germplasm collection. DJ 6514 and the breading lines derived from it become susceptible to sorghum midge in Kenya. Therefore, we evaluated a diverse array of midge-resistant and -susceptible lines at Alupe, Kenya; and ICRISTAT Center, India, to identify lines with stable resistance across seasons and locations. The test material was also evaluated for resistance to leaf diseases at Alupe, Kenya; to identify lines with multiple resistance to sorghum midge and leaf diseases. Across seasons and locations; IS 3461, IS 8884, IS 8887, IS 8891, IS 19476, IS 22806, and AF 28 showed high to moderate levels of resistance to midge, and these lines will be useful for use in resistance breeding programs. Thirty-nine lines showed resistance to midge both under natural infestation and no-choice headcage screening at ICRISTAT Center, India, over four seasons, of which IS 18696, IS 22806, ICSV, 197, ICSV 745, ICSV 88032, PM 20710-2, DJ 6514, and AF 28 were highly resistant. Genotypes IS 3461, IS 8884, IS 8887, IS 8589, IS 19476, IS 22806, ICSV 736, ICSV 90003, and AF 28 showed moderate levels of resistance to both midge and leaf diseases at Alupe, Kenya; and these lines can be used as sources of multiple resistance to these pests. Lines IS 2766, IS 7148, IS 8733, and IS 8589, showed high levels of resistance to leaf diseases in Kenya. Resistance to midge breaks down in some lines at Alupe, Kenya; possibly because of the influence of environment on the expression of resistance or the possible differences in midge populations at different geographic locations.

Breakdown of resistance to sorghum midge, Stenodiplosis sorghicola

Sorghum midge (Stenodiplosis sorghicola Coquillett) is an important pest of grain sorghum worldwide. Several sources of resistance to sorghum midge have been identified in the world sorghum germplasm collection, of which some lines show a susceptible reaction in Kenya. Therefore, we studied the insect density damage relationships for a diverse array of midge-resistant and midge-susceptible sorghum genotypes, and variation in association of glume and grain characteristics with expression of resistance to sorghum midge. AF 28 and IS 8891 showed resistance to sorghum midge both in India and Kenya; DJ 6514 and ICSV 197, which are highly resistant to sorghum midge in India, showed a susceptible reaction at Alupe, Kenya. Sorghum midge damage in general was greater in Kenya than that observed in India at the same level of midge density suggesting that the breakdown of resistance in Kenya is due to factors other than insect density. Glume length, glume breadth, and glume area were positively associated with susceptibility to sorghum midge at both locations. However, under natural infestation, the correlation coefficients were stronger in India than in Kenya. Grain mass at 3 and 6 days after anthesis was positively associated with susceptibility to midge in India, but did not show any association with midge damage in Kenya. Grain growth rate between 3 and 6 days after anthesis was more strongly correlated with susceptibility to midge in Kenya than in India. Variation in the reaction of sorghum genotypes across locations may be partly due to the influence of environment on association between glume and grain characteristics with susceptibility to sorghum midge, in addition to the possible differences in midge populations in different geographical regions.

Spikelet Flowering Time: Cause of Sorghum Resistance to Sorghum Midge (Diptera: Cecidomyiidae)

Resistance of sorghum, Sorghum bicolor (L.) Moench, to sorghum midge, Stenodiplosis sorghicola (Coquillett), has not been well understood. In this study, possible causes of resistance were examined by comparing time of oviposition with times spikelets of resistant and susceptible sorghums flowered and thus were vulnerable to damage. Spikelets of resistant genotypes began flowering during the night, at 0100 hours (CDT), and most were closed and no longer vulnerable by the time sorghum midges began to oviposit in the field at 0800 hours. Peak flowering of resistant sorghums was between 0300 and 0700 hours. Most spikelets of susceptible sorghums, however, were flowering after daylight, at 0800 hours, when sorghum midge abundance began to increase. At 1000 hours, the time most sorghum midges (2.5 per panicle) were in the field, percentages of spikelets penetrable by a pin the diameter of a sorghum midge ovipositor were 32 and 62% for resistant and susceptible sorghums, respectively. Damage to panicles of resistant sorghums averaged 29.6%, whereas susceptible sorghums were more than twice as damaged (68.2%). Delaying for 5 h the daily flowering period of a resistant hybrid to coincide with time of peak sorghum midge abundance in the field resulted in 3.2 times as many sorghum midges emerging and 2.2 times as much damage as to panicles of the resistant hybrid that flowered at the normal time. Damage and numbers of sorghum midges emerging were not significantly different between normal and changed panicles of a susceptible hybrid. Most spikelets of resistant sorghums flowered and closed early and thus evaded damage before ovipositing sorghum midges were in the field. These results support the hypothesis that resistance is caused by asynchrony between time of sorghum spikelet flowering and presence of sorghum midge.

Tritrophic interactions in sorghum, midge ( Stenodiplosis sorghicola) and its parasitoid ( Aprostocetus spp.)

Studies on tritrophic interactions involving sorghum genotypes, midge ( Stenodiplosis sorghicola) and the predominant parasitoids ( Aprostocetus spp.) at ICRISAT Asia Center were conducted using three midge resistant (ICSV 745, ICSV 89058 and IS 10712) and three susceptible (Swarna, CSH 9 and ICSV 112) genotypes during the post-rainy (1992/93) and rainy (1993) seasons. A. coimhatorensis, the predominant parasitoid during post-rainy season, preferred mid-late midge larvae for parasitization, while A. gala, which was predominant during the rainy season, preferred early-mid larval stages. Variations in the preference of A. coimbatorensis and A. gala for the developmental stage of their host larvae indicate good prospects for the biological control of sorghum midge populations. There were significant differences in parasitization level of midge by Aprostocetus spp. between resistant and susceptible sorghum genotypes, and season. Higher parasitization was observed on susceptible genotypes than on resistant ones during both post-rainy and rainy seasons. However, the level of parasitization was greater in post-rainy than in rainy seasons. There was also evidence of higher midge infestation in rainy than in post-rainy seasons. Susceptible genotypes attracted more parasitoids because of high levels of midge infestations. Low parasitoid density in midge resistant sorghum under glasshouse and field conditions was associated with low midge infestations in these genotypes. However, parasitoids were always associated with their host in spite of low midge densities in resistant genotypes. The present study revealed that the interaction between host plant resistance and parasitoids of sorghum midge would thus be synergistic and complementary and could result in successful integration of these two important pest management tactics.

Loss of genetic diversity associated with selection for resistance to sorghum midge in Australian sorghum

In recent years, hybrids with levels of resistance to sorghum midge (Stenodiplosis sorghicola Coquillett) have become available to Australian sorghum producers. These hybrids have been readily accepted to the extent that more than 80% of the sorghum growing area was planted to hybrids with some level of midge resistance by 1995. Since selection for resistance to sorghum midge is one of the primary objectives of Australian sorghum breeding programs, the relationship between resistance and genetic diversity was investigated. Genetic diversity and heterozygosity were assessed using restriction fragment length polymorphism analysis among 26 grain sorghum hybrids grown commercially in Australia. The genetic distances between each sorghum hybrid and a standard highly resistant hybrid were found to be strongly negatively correlated to hybrid midge resistance ratings (r = - 0.77, p < 0.001). In addition, the average heterozygosity of each hybrid was correlated with their midge resistance ratings (r = - 0.54, p < 0.01). The results indicate that the move to midge resistant hybrids has been associated with a narrowing of the genetic diversity and average heterozygosity of commercial sorghum hybrids. Repeated use of particular elite parent lines, linkage drag and genetic drift are likely to have contributed to this decline. This reduction in genetic diversity may have implications for the genetic vulnerability of sorghum in Australia and the rate of progress in breeding for yield.

Emergence Pattern of Sorghum Midge and its Major Parasitoids on Midge-resistant and Susceptible Genotypes

Studies were conducted on the species composition of parasitoids of sorghum midge, Stenodiplosis sorghicola Coquillett (Diptera: Cecidomyiidae), emergence pattern and level of parasitism. They took place at the International Crops Research Institute for the Semi-Arid Tropics Asia Centre using three midge-resistant (ICSV 745, ICSV 89058 and IS 10712) and three susceptible (Swarna, CSH 9 and ICSV 112) genotypes during the 1992-93 post-rainy and 1993 rainy seasons. The species of parasitoids collected were Aprostocetus gala Walker, A. coimbatorensis Rohwer (Hymenoptera: Eulophidae) and Eupelmus spp. (Hymenoptera: Eupelmidae). The species composition varied with the season, but was unaffected by varietal resistance and susceptibility to the midge. Although both species of Aprostocetus were present in rainy and post-rainy seasons, A. gala was predominant during the rainy season whereas A. coimbatorensis was predominant in the post-rainy season. There was no significant difference in the pattern of parasitoid emergence or the level of midge parasitization between resistant and susceptible genotypes. These results indicate that resistance to midge in the genotypes studied was not antagonistic to parasitoid activity, and that there is potential to interface biological control with host-plant resistance in the management of this insect.

Registration of ICS 88019 and ICS 88020 Midge‐Resistant Grain Sorghum A and B Parental Lines

ICSA88019 and ICSB88019 (PI592505) and ICSA88020 and ICSB88020 (PI592506) are sorghum midge (Contarinia sorghicola [Stenodiplosis sorghicola])-resistant sorghum (Sorghum bicolor) seed parents based on the A1 CMS system and developed by ICRISAT at Patancheru, India. ICSB88019 and ICSB88202 were both derived by pedigree selection, and have the pedigrees IS152 × DJ6214-8-1-1-1-1 and FLR101 × DJ6514-13-1-1-2-1, respectively, where DJ6514 is a stable source of resistance to sorghum midge from India, IS152 is a locally adapted germplasm accession from India and FLR101 is an elite line derived from the FLR population. The B-lines were crossed to 296A (A1 cytoplasm) for conversion into male-sterile lines. Information is tabulated on plant height, time to 50% anthesis, grain yield and midge damage of the B-lines grown at Patancheru during the rainy season of 1991 and the post-rainy season of 1991-92.