Resistance to cyst nematode (Heterodera cajani) in pigeonpea cultivars and in wild relatives of Cajanus*

Heterodera cajani is an important nematode pest of pigeonpea in India. Evaluation of 58 pigeonpea cultivars and 61 accessions of Cajanus acutifolius, C. cajanifolius, C. grandifolius, C. lanceolatus, C. lineatus, C. mollis, C. pla-tycarpus, C. reticulatus, C. scarabaeoides, C. sericeus, C. volubilis, Flemingia macrophylla, F. stricta, F. strobilifera, Rhynchosia aurea, R. bracteata, R. cana, R. densiflora, R. minima, R. rothii, R. suaveolens and R. sublobata revealed that the tested pigeonpea cultivars lacked resistance to H. cajani. Eight accessions of wild relatives were resistant and 20 accessions were moderately resistant. Based on the white cyst number on roots and low plant-to-plant variation, two accessions of C. scarabaeoides (ICPWs 111 and 128), three accessions of Flemingia spp. (ICPWs 194, 202 and 203), and one accession each of R. rothii (ICPW 257), R. densiflora (ICPW 224), and R. aurea (ICPW 210) were identified as resistant and promising for use in intergeneric hybridisation programmes.     

A screening technique to evaluate pigeonpea for resistance to Rotylenchulus reniformis*

Rotylenchulus reniformis is one of the most important nematode pests of pigeonpea. A simple greenhouse technique has been developed to aid evaluation of pigeonpea genotypes for resistance to R. reniformis. In greenhouse pot experiments, eggsacs of R. reniformis in pigeonpea (cv. ICPL 87) roots were counted by eye and with the aid of a stereoscopic microscope at 15, 30 and 45 days after seedling emergence in soils infested with various numbers of vermiform R. reniformis. Seedlings were rated for the number of eggsacs per root system on a one (no eggsacs) to nine (more than 50 eggsacs) scale. Eggsac ratings were more uniform when roots were evaluated at 30 – 45 days than at 15 days and an inoculum of 15 to 30 individuals/cm³ soil also helped reduce variability. Eggsacs were not easily visible without the aid of a stereoscopic microscope. Of the 14 stains tested, exposure of nematode-infected roots to 0.25% trypan blue for three min was effective in staining the eggsacs blue without staining the roots. Using the stain, the assessment of infestation by R. reniformis was equally accurate with or without the aid of a stereoscopic microscope. Exposure of eggsacs to trypan blue enhanced the emergence of juveniles from the eggsacs.     

Assessment of variation in Aceria cajani using analysis of rDNA ITS regions and scanning electron microscopy: implications for the variability observed in host plant resistance to pigeonpea sterility mosaic disease

Aceria cajani on pigeonpea (Cajanus cajan) is the vector of the agent of pigeonpea sterility mosaic disease (PSMD), a very damaging virus‐like disease in the Indian subcontinent. PCR was used to amplify A. cajani nuclear ribosomal DNA (rDNA) internal transcribed spacers (ITS) and associated rDNA genes. They were assessed for variation in this genome region by nucleotide sequencing and RFLP. A. cajani‐specific rDNA primers are described. Several A. cajani populations were collected from pigeonpea plants from various PSMD endemic locations in India, Nepal and Myanmar. No significant variation was identified in rDNA regions, or in morphological features. These results suggest strongly that A. cajani on pigeonpea across the Indian subcontinent constitutes one species and that no other Aceria species and probably no A. cajani biotypes that differ in vectoring ability are involved in the transmission of the agent of PSMD. The implications of these findings for the variability observed in PSMD‐resistant pigeonpea genotypes across various locations in India are discussed.     

Temperature Effects on Development and Reproduction of Heterodera cajani on Pigeonpea

Effects of constant and fluctuating temperature on development and reproduction of Heterodera cajani were studied on pigeonpea cv. ICPL 87 in growth chambers at 10, 15, 20, 25, and 30 C and in a greenhouse fluctuating between 22.2 and 37.8 C. Nematode penetration was greatest (P = 0.001) in roots at 25 C; there was no penetration at 10 C. The basal threshold temperature for development was calculated to be 11 C. Completion of one H. cajani generation required 17, 28, 35, and 66 days (323, 392, 315, and 264 degree-days) at 30, 25, 20, and 15 C, respectively, and 19 days (356 degree-days) at a fluctuating temperature. Survival was greater at 20 and 25 C than at 15 and 30 C. The greatest (P = 0.05) number of females (17.9 females per root) were produced at 25 C, compared with 13.2 at 20 C, 7.9 at 30 C, and 2.5 females at 15 C. Nematode reproduction was 1.6 to 7.1 times greater at 25 C than at other temperatures. Emergence of juveniles from egg sacs and cysts was greater at 25 and 30 C than at 15 and 20 C. Equations were developed to predict nematode development rate, cumulative juvenile emergence from egg sacs and cysts, and population increases as influenced by temperature.     

Regulation of Population Densities of Heterodera cajani and Other Plant-Parasitic Nematodes by Crop Rotations on Vertisols,in Semi-Arid Tropical Production Systems in India

The significance of double crop (intercrop and sequential crop), single crop (rainy season crop fallow from June to September), and rotations on densities of Heterodera cajani, Helicotylenchus retusus, and Rotylenchulus reniformis was studied on Vertisol (Typic Pellusterts) between 1987 and 1993. Cowpea (Vigna sinensis), mungbean (Phaseolus aureus), and pigeonpea (Cajanus cajan) greatly increased the population densities of H. cajani and suppressed the population densities of other plant-parasitic nematodes. Mean population densities of H. cajani were about 8 times lower in single crop systems than in double crop systems, with pigeonpea as a component intercrop. Plots planted to sorghum, safflower, and chickpea in the preceding year contained fewer H. cajani eggs and juveniles than did plots previously planted to pigeonpea, cowpea, or mungbean. Continuous cropping of sorghum in the rainy season and safflower in the post-rainy season markedly reduced the population density of H. cajani. Sorghum, safflower, and chickpea favored increased population densities of H. retusus. Adding cowpea to the system resulted in a significant increase in the densities of R. reniformis. Mean densities of total plant-parasitic nematodes were three times greater in double crop systems, with pigeonpea as a component intercrop than in single crop systems with rainy season fallow component. Cropping systems had a regulatory effect on the nematode populations and could be an effective nematode management tactic. Intercropping of sorghum with H. cajani tolerant pigeonpea could be effective in increasing the productivity of traditional production systems in H. cajani infested regions.     

Screen of safflower (Carthamus tinctorius L.) genotypes against Phytophthora drechsleri and Fusarium solani,the causal agents of root rot disease

Safflower (Carthamus tinctorius L.) plants were affected by a severe root rot disease caused by Phytophthora drechsleri and Fusarium solani in Isfahan province of Iran during 2005–2007. Disease incidence was more than 30% in severely infected fields. Twenty-one safflower genotypes, including six local cultivars and 15 internal pure lines were evaluated for their resistance to root rot disease in laboratory and greenhouse conditions. Safflower seedlings were evaluated for lesion length on infected roots in laboratory, as well percentage of live seedlings in greenhouse. The results indicated a high negative correlation between lesion length on roots and percentage of live seedlings. The most resistant and susceptible genotypes to P. drechsleri were identified as pure line Karaj row 12 (KW12) and cultivar Koseh with lesion lengths of 10.01 and 15.51?mm on roots and 45.60 and 18.00% live seedlings, respectively. The most resistant genotype to F. solani was identified as pure line KW11 with a lesion length of 9.31?mm on roots as well 62.80% live seedlings. The most susceptible genotypes were identified as cultivar Koseh and pure lines KW2 and KW3 with lesion lengths of 13.29, 12.72 and 12.13?mm on roots and 25.60, 28.40 and 28.40% live seedlings, respectively. The most resistant genotypes to both P. drechsleri and F. solani were identified as pure lines KW15 and KW9 with a 55.40% live seedlings. The most susceptible genotypes were cultivars Koseh, Goldasht and pure lines KW6, KW3 and KW2 with 35.40, 35.40, 35.40, 37.60 and 37.60% live seedlings in greenhouse, respectively.     

Effects of Resistance in White Clover (Trifolium repens) on Heterodera trifolii

Clones of two partially resistant and two susceptible white clover, Trifolium repens, genotypes were exposed to eggs of Heterodera trifolii and nematode development in stained roots measured at 2, 4, 7, 11, 18, 23, and 37 days after inoculation. The differences in development between nematode populations in resistant and susceptible genotypes showed that resistance operated after infection during feeding and development. At 7 days after inoculation, counts of second-stage juveniles did not differ between genotypes, whereas at 37 days more adults had developed in the susceptible than in the resistant genotypes. In a separate experiment, cysts hosted by susceptible genotypes were larger and contained more eggs than those on resistant genotypes so that the product of the values for cysts per plant and for eggs per cyst resulted in a more sensitive measure of resistance than from using cysts per plant alone.     

Evaluation of Trichoderma spp. from central and northern regions of Turkey for suppression of Polymyxa betae as a vector of rhizomania disease

In the current study, 18 Trichoderma spp. isolates were obtained from different provinces in central and northern regions of Turkey. The ability of nine selected isolates to suppress the colonisation of roots by P. betae and the multiplication of BNYVV in sugar beet roots under controlled conditions were tested. Roots of seedlings growing in the P. betae-BNYVV-infested soil were analysed by enzyme-linked immunosorbent assay to test for the presence of BNYVV and checked microscopically for the density of cystosori of P. betae. The numbers of P. betae resting spores in cystosori for each treatment were counted using a light microscope. Except for isolates Tr-1 and Tr-5, the effect of selected Trichoderma isolates on suppressing multiplication of BNYVV varied between 4 and 53%. The total number of resting spores in the roots varied between 14.4 and 25.1 for the different Trichoderma spp. treatments. The lowest number of resting spores in clusters was recorded in T. harzianum Tr-8. In addition, the shapes of resting spores were not normal in the Tr-8 treatments. The cystosori from this treatment were also abnormally dark in colour and had deformed walls.     

Temperature and seedling age affect susceptibility of perennial ryegrass seedlings to pathogenic fungi

Summary Effects of temperature and seedling age on survival of perennial ryegrass (Lolium perenne L.) seedlings grown on sand-wheat wholemeal cultures of different isolates ofFusarium spp. (9 isolates),Pythium spp. (9 isolates), andChaetomium spp. (1 isolate) are reported. Some isolates were virulent over the whole range of temperatures tested (7.5–27.5°C). The virulence of others depended on temperature. Most isolates were less virulent at intermediate temperatures (12.5–22.5°C) than at higher or lower temperatures. At 25°C ryegrass seedlings were susceptible to fungal attack for only a limited period after germination commenced. This period differed for different fungi, but for most isolates tested, seedlings were resistant after 2–3 days.     

Tolerance to reniform nematode (Rotylenchulus reniformis) race A in pigeonpea (Cajanus cajan) genotypes

The reniform nematode (Rotylenchulus reniformis) is an important pathogen of pigeonpea (Cajanus cajan). Forty‐six medium maturity (mature in 151–200 days at Patancheru, India) pigeonpea genotypes were evaluated for resistance and tolerance to the reniform nematode in greenhouse and field tests, over the period 1990–97. Each genotype was screened for number of nematode egg masses on a 1 (no egg mass = highly resistant) to 9 (> 50 egg masses = highly susceptible) scale. Plant biomass production in carbofurantreated plots was compared with that in non‐treated plots in a field naturally infested with R. reniformis. Pigeonpea genotypes C 11, ICPL 87119 and ICPL 270 were used as nematode susceptible checks. Genotypes with good plant growth, both in nematode‐free and nematode‐infested plots, were identified as tolerant and evaluated for plant growth and yield for at least three years. All the tested genotypes were susceptible (7 and 9 egg mass score). Single‐plant‐selections, based on plant vigour and yield, were made from genotypes showing tolerance to nematode infection. The level of tolerance was enhanced by plant‐to‐progeny row selection for plant vigour and seed yield in a nematode‐sick field for at least three years. The most promising nematode tolerant genotypes produced significantly greater yield and biomass than the locally grown pigeonpea cultivars in fields naturally infested with R. reniformis at two locations. Pigeonpea landraces are considered to be the most likely sources of tolerance to the nematode. These reniform nematode tolerant lines represent new germplasm and they are available in the genebank of pigeonpea at ICRISAT bearing accession numbers ICP 16329, ICP 16330, ICP 16331, ICP 16332, and ICP 16333.     

Evaluation of fluorescent Pseudomonads and <Emphasis Type="Italic">Bacillus</Emphasis> isolates for the biocontrol of a wilt disease complex of pigeonpea

Summary Twenty isolates of fluorescent pseudomonads and Bacillus spp. were obtained from pathogen suppressive soil of a pigeonpea (Cajanus cajan) field showing wilt disease complex. These isolates were evaluated in the laboratory and screen-house for the biocontrol of wilt disease complex. Six isolates were considered to have potential for the biocontrol of the disease on the basis of antibiotic sensitivity, antifungal activity, fluorescence produced by Pseudomonas, inhibitory effect on the hatching and penetration of nematodes and colonization of pigeonpea roots by these isolates. These isolates will be further tested for their biocontrol of wilt disease complex of pigeonpea under field conditions.     

Structure of Syncytia Induced by Heterodera avenae Woll. in Roots of Susceptible and Resistant Wheat (Triticum aestivum L.)

The structure of syncytia induced by Heterodera avenae in roots of susceptible Triticum aestivum cv. ‘Capa’ and resistant wheat AUS 10894 was investigated. In susceptible plants the first syncytia were observed 4 days after placing the seedlings into a substrate containing nematode cysts. They were located on different root levels. In resistant plants syncytia were first found after 14 days, exclusively in the root maturity zone. In both wheats syncytia consisted mostly of stelar parenchymatic cells. The syncytia induced in roots of Triticum aestivum AUS 10894 were characterized by less immediate contact with the host tracheary elements than the syncytia induced in roots of susceptible Triticum aestivum cv. ‘Capa’. In both wheats a stimulation of pericycle cell divisions, giving rise to lateral roots, was found in parts where the syncytia developed.     

Infectivity,Development, and Reproduction of Heterodera cajani on Pigeonpea: Influence of Soil Moisture and Temperature

The effect of soil moisture on penetration, development, and reproduction of Heterodera cajani on pigeonpea (cv. ICPL 87) was investigated in growth chambers held at 20 and 25 C, and in a greenhouse where temperature fluctuated between 25 and 32 C. Averaged across temperatures, the percentage of juveniles that penetrated roots was 34.3, 31.8, 8.8, and 3.7% at 24, 32, 16, and 40% soil moisture levels, respectively. Numbers of females per root system 4 weeks after infesting soil with second-stage juveniles was 79.6 at 24%, 65.3 at 32%, 26.1 at 16%, and 2.9 at 40% soil moisture. Nematode reproduction was greatest (P = 0.001) at 24% soil moisture and 25 C. Reproductive factor was 19.4 at 24%, 15.2 at 32%, 5.7 at 16%, and 0.5 at 40% soil moisture level. Nematode penetration, development, and reproduction at different moisture levels were greater (P = 0.01) at 25 and 25-32 C than at 20 C. Plant growth was retarded at 40% soil moisture and 20 C in comparison to that at 24 and 32% moisture levels and 25 C. This information on influence of temperature and soil moisture will be helpful in developing models for predicting changes in H. cajani densities in pigeonpea fields during rainy and postrainy dry seasons in the semi-arid tropics.     

Role of catalase,H2O2 and phenolics in resistance of pigeonpea towards Helicoverpa armigera (Hubner)

Rapid generation of superoxide radicals and accumulation of H₂O₂ is a characteristic early response of plants following perception of insect herbivory signals. Induction of oxidative burst on account of herbivory triggers various defense mechanisms in plants. Response of superoxide and H₂O₂-metabolizing enzymes and secondary metabolites in nine pigeonpea genotypes to Helicoverpa armigera feeding was investigated. Out of nine, four genotypes were found to be moderately resistant, three were intermediate and two were moderately susceptible. In general, H. armigera infestation resulted in increase in superoxide dismutase activity, H₂O₂ and phenolics content and decrease in catalase (CAT) activity in leaves, developing seeds and pod wall of pigeonpea genotypes. Peroxidase activity was found only in leaves. Among genotypes, the increase in phenolic constituents was found greater in moderately resistant genotypes than in moderately susceptible genotypes; this might determine their contribution in providing resistance to genotypes against H. armigera infestation. The capability of moderately resistant genotypes to maintain relatively lower H₂O₂ content and higher CAT activity in pod wall and developing seeds also appeared to determine resistance of genotypes towards H. armigera. Expression of resistance to H. armigera was found to be associated with a negative correlation of H₂O₂-metabolizing enzymes and phenolics with pod damage as well as with negative association between CAT activity and H₂O₂ content. A positive correlation found between H₂O₂ content and pod damage suggested the accumulation of H₂O₂ in response to pod borer attack. In addition, correlation analysis also revealed a positive association between CAT, phenolic compounds and DPPH radical scavenging activity following pod borer attack; this indicated their contribution in resistance mechanisms against H. armigera herbivory.     

Insights into Salt Stress-Induced Biochemical,Molecular and Epigenetic Regulation of Spatial Responses in Pigeonpea (Cajanus cajan L.)

Pigeonpea (Cajanus cajan L.) is a rich source of nutritionally good quality proteins, carbohydrates, minerals, and vitamins. However, environmental stresses adversely affect its productivity. Only limited reports are available on biochemical/physiological responses of pigeonpea under salt stress. The objectives of the present study were to screen pigeonpea germplasm accessions for salt stress tolerance, followed by understanding their biochemical, epigenetic and molecular responses. Based on germination, growth, and vigor of seedlings under salt stress, the most contrasting pair of salt-responsive genotypes (ICP1071- most salt-sensitive, and ICP7- most salt-tolerant) were selected. Three-week-old seedlings subjected to 250 mM NaCl stress for 7 days showed a significant increase in proline and reducing sugar contents in the case of ICP7, whereas a considerable increase in cell wall-degrading enzyme activity and protein oxidation was observed in ICP1071. Superoxide dismutase, peroxidase, and glutathione reductase activity increased considerably in shoots of ICP7. We observed the CcCYP gene to be upregulated in root, whereas CcCDR was upregulated in shoots of the salt-tolerant genotype to provide protection against the stress. The extent of DNA hypomethylation in the contrasting pigeonpea genotypes under salt stress was correlated with their salt tolerance level. Bisulfite sequencing of CcCDR revealed that methylation of three cytosine residues in CHH context in shoots of the ICP7 genotype due to salt stress results in 2.6-fold upregulated expression of the gene. With a 6.8% increase in methylation of the coding region of CcCDR, its expression level increased by 22%. To the best of our knowledge, this is the first report on a comprehensive study of salt-induced biochemical, epigenetic and molecular responses of pigeonpea, which might be useful in the development of improved salt-tolerant variety.

     

Resistance to cucumber mosaic virus in potato

Reactions to two subgroup I isolates (Fny-CMV and Pf-CMV) and two subgroup II isolates (A9-CMV and LS-CMV) of cucumber mosaic virus (CMV) were studied in three non tuber-bearing wild potato species (Solanum spp.) of the series Etuberosa, and in two tuber-bearing interspecific potato hybrids and four potato cultivars using graft-inoculation. Three classes of phenotypic reactions (susceptible, hypersensitive, extreme resistance) were observed in the tuber-bearing genotypes. Susceptible genotypes developed mosaic or severe mosaic with leaf malformation and had high CMV titres. Hypersensitive genotypes developed either top necrosis or vein necrosis and/or necrotic spots on apical leaves, and had low CMV titres. Extremely resistant genotypes had no symptoms and no CMV was detected. The hybrid 87HW13.7 (S. tuberosum×S. multidissectum) developed top necrosis specific to infection with Fny-CMV. The hybrid ‘A6’ (S. demissum×S. tuberosum cv. Aquila) was hypersensitive to all CMV isolates tested. Extreme resistance was not functional against all CMV isolates. Neither hypersensitivity nor extreme resistance were related to the CMV subgroup.     

Morphological and chemical components of resistance to pod borer, Helicoverpa armigera in wild relatives of pigeonpea

Host plant resistance is an important component for minimizing the losses due to the pod borer, Helicoverpa armigera, which is the most devastating pest of pigeonpea. An understanding of different morphological and biochemical components of resistance is essential for developing strategies to breed for resistance to insect pests. Therefore, we studied the morphological and biochemical components associated with expression of resistance to H. armigera in wild relatives of pigeonpea to identify accessions with a diverse combination of characteristics associated with resistance to this pest. Among the wild relatives, oviposition non-preference was an important component of resistance in Cajanus scarabaeoides, while heavy egg-laying was recorded on C. cajanifolius (ICPW 28) and Rhynchosia bracteata (ICPW 214). Accessions belonging to R. aurea, C. scarabaeoides, C. sericeus, C. acutifolius, and Flemingia bracteata showed high levels of resistance to H. armigera, while C. cajanifolius was as susceptible as the susceptible check, ICPL 87. Glandular trichomes (type A) on the calyxes and pods were associated with susceptibility to H. armigera, while the non-glandular trichomes (trichome type C and D) were associated with resistance to this insect. Expression of resistance to H. armigera was also associated with low amounts of sugars and high amounts of tannins and polyphenols. Accessions of wild relatives of pigeonpea with non-glandular trichomes (type C and D) or low densities of glandular trichomes (type A), and high amounts of polyphenols and tannins may be used in wide hybridization to develop pigeonpea cultivars with resistance to H. armigera. Handling editor: Robert Glinwood     

Detached leaf assay to screen for host plant resistance to Helicoverpa armigera

The noctuid Helicoverpa armigera (Hübner) is a major insect pest of chickpea Cicer arietinum L., pigeonpea Cajanus cajan (L.) Millsp., peanut Arachis hypogaea L., and cotton Gossypium spp., and host plant resistance is an important component for managing this pest in different crops. Because of variations in insect density and staggered flowering of the test material, it is difficult to identify cultivars with stable resistance to H. armigera across seasons and locations. To overcome these problems, we standardized the detached leaf assay to screen for resistance to this pest in chickpea, pigeonpea, peanut, and cotton under uniform insect pressure under laboratory conditions. Terminal branch (three to four fully expanded leaves) of chickpea, first fully expanded leaf of cotton, trifoliate of pigeonpea, or quadrifoliate of peanut, embedded in 3% agar-agar in a plastic cup/jar of appropriate size (250-500-ml capacity) infested with 10-20 neonate larvae can be used to screen for resistance to H. armigera. This technique keeps the leaves in a turgid condition for approximately 1 wk. The experiments can be terminated when the larvae have caused > 80% leaf damage in the susceptible check or when differences in leaf feeding between the resistant and susceptible checks are maximum. Detached leaf assay can be used as a rapid screening technique to evaluate germplasm, segregating breeding materials, and mapping populations for resistance to H. armigera in a short span of time with minimal cost, and under uniform insect infestation. It also provides useful information on antibiosis component of resistance to the target insect pest.     

Field evaluation of insect resistance in a wild tomato and its effects on insect parasitoids

Populations ofHelicoverpa (=Heliothis) zea (Boddie),Heliothis virescens (F.),Manduca sexta (L.) andM. quinquemaculata (Haw.) and their egg and larval parasitoids were sampled in field plots of the: insect-resistant wild tomato,Lycopersicon hirsutum f. glabratum C. H. Mull, accession PI 134417; susceptible commercial tomato cultivar ‘Better Boy’; F₁ hybrid; and selected, moderately resistant backcross genotype. Densities ofH. zea andH. virescens eggs and small larvae were higher on resistant genotypes than on susceptible genotypes, but densities of large larvae were similar on all genotypes. Densities ofManduca spp. larvae were too low to permit similar analyses of the effects of plant genotype. Rates of egg parasitism byTrichogramma spp. andTelenomus sphingis (Ashmead) were reduced on insect-resistant genotypes. Rates of parasitism by the larval parasitoidsCampoletis sonorensis (Cameron) andCotesia congregata (Say) were reduced on resistant genotypes. No consistent effects on parasitism rates byCotesia marginiventris (Cresson) were observed and parasitism rates byCardiochiles nigriceps Viereck were unaffected.     

Trichogramma egg parasitism ofHelicoverpa armigera on short-duration pigeonpea intercultured with sorghum

The levels of egg parasitism byTrichogramma spp. (Hymenoptera: Trichogrammatidae) on populations ofHelicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) were recorded on sorghum (Sorghum bicolor L.) and on two flushes of flowers on short-duration pigeonpea (Cajanus cajan L.).H. armigera oviposition was concentrated on the early flowering stage of sorghum and the flowering and early podding stages of both flushes of pigeonpea. Parasitism on sorghum increased rapidly as egg density increased and reached a peak of 74.6%. Parasitism on pigeonpea was concentrated onH. armigera eggs laid on the first flush of pigeonpea flowers with a maximum of 69.2%. These high levels of parasitism on pigeonpea coincided with the period of parasite activity on sorghum. The levels of parasitism then declined rapidly and only very low levels were detected on a second flush of flowers. This rapid decline resulted in the overall egg mortality caused byTrichogramma on pigeonpea to be low, with a maximum of 7.8% caused by parasitism, compared to 34.4% on sorghum. The pattern of parasitism suggests that a transfer of parasites occurred from sorghum to pigeonpea. The rapid decline of parasitism on the pigeonpea indicates that parasite populations cannot be sustained on pigeonpea once the influx from sorghum stops. The results are discussed in terms of a possible method of encouraging the transfer of parasites from sorghum to short-duration pigeonpea by producing a more continuous cropping environment.