Levels of tolerance, antibiosis, and antixenosis among resistant buffalograsses and zoysiagrasses

The western chinch bug, Blissus occiduus Barber, has been documented as one of the most serious pests of buffalograss, Buchlo? dactyloides (Nuttall) Engelmann, and zoysiagrass, Zoysia japonica Steudel, grown for turf in midwestern states. Resistance to the western chinch bug has been identified in both buffalograsses and zoysiagrasses. Choice and no-choice studies were conducted to determine the categories (antibiosis, antixenosis, and tolerance) of three resistant buffalograsses (PX3-5-1', 196', and 184') and three resistant zoysiagrasses (El Toro, Emerald, and Zorro). Antibiosis studies found no significant differences in survival, nymphal development, or fecundity among the resistant and susceptible buffalograsses or zoysiagrasses, indicating that antibiosis is not an important factor in the resistance. Based on chinch bug damage ratings, 184, 196, and PX3-5-1 have comparable levels of tolerance to the known tolerant buffalograss 'Prestige', and Zorro was the most tolerant zoysiagrass. Choice studies indicated the presence of antixenosis in the buffalograss selection 196 and the zoysiagrass Emerald.     

Chinch bug-resistant buffalograss: an investigation of tolerance, antixenosis, and antibiosis

Choice and no-choice studies were conducted to determine the categories (antibiosis, antixenosis, and tolerance) of resistance of four buffalograsses (NE91-118, 'Bonnie Brae', 'Cody', and 'Tatanka') previously identified as resistant to the western chinch bug, Blissus occiduus Barber. Antibiosis studies found no significant differences in western chinch bug fecundity, nymphal development, or survival among the resistant and susceptible buffalograsses. Tolerance studies indicated that NE91-118, Cody, and Tatanka exhibited moderate-to-high levels of tolerance based on western chinch bug damage ratings and plant height, whereas Bonnie Brae exhibited moderate-to-low levels of tolerance. Choice studies indicated the presence of antixenosis in NE91-118, whereas Cody and Tatanka showed little or no antixenosis. Scanning electron microscopy was used to disclose morphological differences between NE91-118 (resistant) and '378' (susceptible). The epicuticular wax structures and trichome densities were similar between 378 and NE91-118, suggesting that morphological structures do not contribute to NE91-118 antixenosis.     

Phenotypic mechanisms of host resistance against greenbug (Homoptera: Aphididae) revealed by near isogenic lines of wheat

Interactions between biotype E greenbug, Schizaphis graminum (Rondani), and wheat, Triticum aestivum L., were investigated using resistant and susceptible near isogenic lines of the greenbug resistance gene Gb3. In an antixenosis test, the greenbugs preferred susceptible plants to resistant ones when free choice of hosts was allowed. Aphid feeding resulted in quick and severe damage to susceptible plants, which seemed to follow a general pattern spatially and was affected by the position where the greenbugs were initially placed. Symptom of damage in resistant plants resembled senescence. Within-plant distribution of aphids after infestation was clearly different between the two genotypes. Significantly more greenbugs fed on the first (oldest) leaf than on the stem in resistant plants, but this preference was reversed in the susceptible one. After reaching its peak, aphid population on the susceptible plants dropped quickly. All susceptible plants were dead in 10-14 d after infestation due to greenbug feeding. Aphid population dynamics on resistant plants exhibited a multipeak curve. After the first peak, the greenbug population declined slowly. More than 70% of resistant plants were killed 47 d after infestation. Performance of both biotype E and I greenbugs on several Gb3-related wheat germplasm lines were also examined. It seems that the preference-on-stem that was characteristic of biotype E greenbugs on the susceptible plants was aphid biotype- and host genotype-dependent. Results from this study suggested that antixenosis, antibiosis, and tolerance in the resistant plants of wheat might all contribute to resistance against greenbug feeding.     

Resistance to Diaphania hyalinata (Lepidoptera: Crambidae) in Cucumis species.

Diaphania hyalinata (L.), the melonworm, causes economic damage in cucurbit species in the Caribbean region. To control larvae feeding on leaves, frequent pesticide applications are needed, but this favors outbreaks of other pests. We looked for plant resistance to D. hyalinata in Cucumis melo L. and two wild Cucumis, C. metuliferus Meyer and C. pustulatus Naudin. Fifteen genotypes were observed using a 1-81 damage scale during 8 wk in two field trials in Guadeloupe, French West Indies. Among the C. melo genotypes, we observed different levels of damage (scores of 32-74 at the maximum damage date) ranging from partially resistant to susceptible genotypes. Both wild species scored <20 at the maximum damage date, and were more resistant in the field tests than the tested genotypes of C. melo. Five C melo genotypes and one C. pustulatus genotype were tested using a detached leaf test. Under controlled conditions, newly hatched larvae were fed with leaves from plants that were 5-9 wk old. Duration and mortality of immature stages were highly correlated. Strong antibiosis (long development and high mortality) was expressed by PI 140471 and Concombre Chien (two C. melo genotypes). For both genotypes, mortality was at least 87.9 versus 34% for Védrantais, a susceptible genotype. Because antibiosis and field resistance were not correlated, we hypothesize that some genotypes expressed antixenosis in the field trials. In addition, possibilities of breeding for C. melo resistance to D. hyalinata is discussed.     

Mechanisms of resistance to Helicoverpa armigera and introgression of resistance genes into F1 hybrids in chickpea

The noctuid pod borer, Helicoverpa armigera is a major pest of chickpea, and host plant resistance is an important component for managing this pest. We evaluated a set of diverse chickpea genotypes with different levels of resistance to H. armigera, and their F₁ hybrids for oviposition non-preference, antibiosis, and tolerance components of resistance under uniform insect infestation under greenhouse/laboratory conditions. The genotypes ICC 12476, ICC 12477, ICC 12478, ICC 12479, and ICC 506EB were non-preferred for oviposition under no-choice, dual-choice, and multi-choice conditions, and also suffered lower leaf damage in no-choice tests as compared to the susceptible check, ICCC 37. Antibiosis expressed in terms of low larval weights was observed in insects reared on ICC 12476, ICC 12478, and ICC 506EB. Weight gain by the third-instars was also low on ICC 12476, ICC 12477, ICC 12478, ICC 12479, and ICC 506EB at the podding stage. Non-preference for oviposition and antibiosis (poor larval growth) were also expressed in hybrids based on ICC 12477, ICC 12476, ICC 12478, ICC 12479, and ICC 506EB as compared to the hybrids based on the susceptible check, ICCC 37, indicating that oviposition non-preference and antibiosis in the F₁ hybrids is influenced by the parent genotype. Loss in grain yield was lower in ICC 12477, ICC 12478, ICC 12479, and ICC 506EB compared to that on ICCC 37. The genotypes ICC 12477, ICC 12478, ICC 12479, and ICC 506EB showing antixenosis, antibiosis, and tolerance mechanism of resistance to H. armigera can be used for developing chickpea cultivars for resistance to this pest.     

Categories of resistance to greenbug (Homoptera: Aphididae) biotype I in Aegilops tauschii germplasm

Categories of resistance to greenbug, Schizaphisgraminum (Rondani), biotype I, were determined in goatgrass, Aegilops tauschii (Coss.) Schmal., accession 1675 (resistant donor parent), 'Wichita' wheat, Triticum aestivum L., (susceptible parent), and an Ae. tauschii-derived resistant line, '97-85-3'. Antibiosis was assessed using the intrinsic rate of increase (rm) of greenbugs confined to each of the three genotypes. Neither parent nor the resistant progeny expressed antibiosis. Mean rm values for greenbug I on Wichita (0.0956), and Ae. tauschii (0.10543) were not significantly different. Mean rm values for Wichita and 97-85-3 were also not significantly different. Antixenosis was determined by allowing aphids a choice to feed on plants of each of the three genotypes. Ae. tauschii 1675 exhibited antixenosis, but this resistance was not inherited and expressed in '97-85-3'. In experiments comparing Wichita and Ae. tauschii 1675, greenbug I population distributions were not significantly different on Wichita at 24 h, but were shifted toward Wichita at 48 h. In the second antixenosis experiment, there were no significant differences in greenbug I population distributions on 97-85-3 or Wichita at 24 or 48 h. When all three lines were compared, there were no significant differences in greenbug biotype I populations at 24 or 48 h after infestation. Comparisons of proportional dry plant weight loss (DWT) and SPAD meter readings were used to determine tolerance to greenbug I feeding. Ae. tauschii 1675 and 97-85-3 were highly tolerant compared with Wichita. Infested and uninfested Ae. tauschii 1675 DWT was nonsignificant, and infested Wichita plants weighed significantly less than uninfested plants. When Wichita and 97-85-3 were contrasted, DWT of infested and uninfested Wichita plants were significantly different, but those of 97-85-3 were not. Mean percent leaf chlorophyll losses for the three genotypes, as measured by the SPAD chlorophyll meter, were as follows: Wichita = 65%; Ae. tauschii 1675 = 25%; and 97-85-3 = 39%. Percent leaf chlorophyll losses caused by greenbug feeding was significantly different in comparisons between Wichita and Ae. tauschii 1675, and comparisons between Wichita and 97-85-3, although feeding damage was not significantly different in comparisons between Ae. tauschii 1675 and 97-85-3. These data provided further evidence of the expression of tolerance to greenbug feeding in Ae. tauschii 1675 and 97-85-3.     

Resistance of wheat lines to Rhopalosiphum padi (Hemiptera: Aphididae) under laboratory conditions

Bird cherry-oat aphid, Rhopalosiphum padi (L.), a polyphagous species with a nearly worldwide distribution, is an important pest of wheat as well as the main vector of barley yellow dwarf virus. We evaluated the resistance categories of eight wheat lines including antibiosis, antixenosis, and tolerance against R. padi under laboratory conditions. The wheat lines tested were ERWYT 88-8, ERWYT 87-6, and ERWYT 87-4 (resistant); ERWYT 87-1, ERWYT 87-20, and ERWYT 88-11 (susceptible); ERWYT 88-12 and ERWYT 88-13 (intermediate). In the antibiosis experiment, R. padi produced fewest progeny on ERWYT 88-8, ERWYT 87-6, and ERWYT 87-4 in reproduction period. In the antixenosis test, R. padi performed best on ERWYT 87-1, ERWYT 87-20, and ERWYT 88-11. Fewer apterous aphids selected ERWYT 88-8, ERWYT 87-4, and ERWYT 87-6 lines indicating antixenosis of these lines to R. padi. In tolerance experiments, however growth parameters differed between treated and untreated seedlings of wheat lines with 10 aphids per day infestation during 21-d period, but not among eight wheat lines. The plant resistance index values were greatest for ERWYT 88-8 (9.71), followed by ERWYT 87-4 (7.04) and ERWYT 87-6 (4.76). ERWYT 88-8, ERWYT 87-6, and ERWYT 87-4 may be important sources of R. padi resistance for small grain breeding and integrated pest management programs.     

Comparison of categories of resistance in wheat and barley genotypes against biotype 2 of the Russian wheat aphid, Diuraphis noxia (Kurdjumov)

The Russian wheat aphid Diuraphis noxia (Kurdjumov) (Homoptera: Aphididae) is a global pest of wheat and barley. This arthropod is difficult to manage with pesticides or biological control agents due to the aphid’s ability to seek shelter in rolled leaves and also to develop virulent biotypes. During the past 20 years, the use of aphid-resistant cereal cultivars has proven to be an economically and ecologically beneficial method of protecting crops from D. noxia damage. Our research reports the results of experiments to determine the categories of D. noxia biotype 2 resistance present in Cereal Introduction Triticeae (CItr) 2401, and a barley genotype (IBRWAGP4-7), compared to control resistant and susceptible wheat and barley genotypes. CItr2401 and IBRWAGP4-7 exhibit no antixenosis, but both genotypes demonstrated antibiosis to D. noxia in the form of reduced aphid populations. Reduced leaf dry weight change, a measure of plant tolerance of D. noxia feeding, was significantly less in CItr2401 and IBRWAGP4-7 plants than in plants of susceptible control varieties. However, tolerance was negated when a tolerance index was calculated to correct for differences in aphid populations. Barley IBRWAGP4-7 is a new source of D. noxia biotype 2 resistance. D. noxia foliar leaf damage and population growth were significantly less on IBRWAGP4-7 plants than on plants of the susceptible barley variety Morex. IBRWAGP4-7 plants were equal in resistance to plants of the resistant barley STARS 9301 and wheat genotype CItr2401. Handling editor: Heikki Hokkanen     

Categories of resistance to greenbug (Homoptera: Aphididae) biotype K in wheat lines containing Aegilops tauschii genes

The wheat lines (cultivars) 'Largo', 'TAM110', 'KS89WGRC4', and 'KSU97-85-3' conferring resistance to greenbug, Schizaphis graminum (Rondani), biotypes E, I, and K were evaluated to determine the categories of resistance in each line to greenbug biotype K. Our results indicated that Largo, TAM110, KS89WGRC4, and KSU97-85-3 expressed both antibiosis and tolerance to biotype K. Largo, KS89WGRC4, and KSU97-85-3, which express antixenosis to biotype I, did not demonstrate antixenosis to biotype K. The results indicate that the same wheat lines may possess different categories of resistance to different greenbug biotypes. A new cage procedure for measuring greenbug intrinsic rate of increase (r(m)) was developed, by using both drinking straw and petri dish cages, to improve the efficiency and accuracy of r(m)-based antibiosis measurements.     

Antixenosis and antibiosis of common beans to Thrips palmi Karny (Thysanoptera: Thripidae)

Antixenosis and antibiosis in the resistance of common beans (Phaseolus vulgaris L.) to the melon thrips, Thrips palmi Karny, were investigated under laboratory and field conditions. Experiments were conducted for four moderately resistant genotypes ('Brunca', BH-130, EMP 486, and FEB 115) in comparison with one susceptible genotype (APN 18). Multiple-choice tests recorded most thrips on EMP 486 and least on FEB 115. Dual-choice tests conducted in both laboratory and field confirmed the antixenotic effect of FEB 115 and the attractant effect of EMP 486 on thrips. These results demonstrate the significance of antixenosis in the resistance of common beans to T. palmi. Life-table studies showed significant differences in egg duration, immature and adult survivorship, female body length and longevity, daily oviposition rate, and total fecundity among the bean genotypes. The intrinsic rate of natural increase (r(m)) and its associated population parameters varied significantly with the bean genotype on which T. palmi cohorts were reared. Based on mean r(m) values, the five bean genotypes can be divided into two groups, with BH-130 and 'Brunca' being less favorable for the population growth of thrips than EMP 486 and FEB 115; the latter were comparable to the susceptible genotype APN 18. These life-table results indicate the role of antibiosis in enhancing the resistance of common beans to T. palmi.     

Categories and inheritance of resistance to Nilaparvata lugens (Hemiptera: Delphacidae) in mutants of indica rice 'IR64'

Varietal mutants can be useful for developing durable resistance, understanding categories of resistance, and identifying candidate genes involved in defense responses. We used mutants of rice 'IR64' to isolate new sources of resistance to the planthopper Nilaparvata lugens (St?l) (Hemiptera: Delphacidae). We compared two mutants that showed a gain and loss of resistance to N. lugens, to determine the categories of resistance to this pest. Under choice tests, female planthoppers avoided settling and laid fewer eggs on the resistant mutant 'D518' than on the susceptible mutant D1131, susceptible check 'TN1', and wild-type IR64, indicating that antixenosis was the resistance category. Similarly, under no-choice conditions, planthoppers laid 29% fewer eggs in D518 than in IR64, but they oviposited more in 'D1131' and TN1. Honeydew excretion was greater on D1131 seedlings but slightly lower on D518 than on IR64. Nymphal survival and adult female weight did not differ among rice cultivars. D518 showed higher tolerance of N. lugens infestations than IR64. Genetic analysis of the F1, F2, and F3 populations derived from D518 x IR64 revealed that resistance in D518 is dominant and controlled by a single gene. Despite the variation in resistance to N. lugens, both mutants and IR64 performed similarly in the field. The mutant D518 is a new source of durable resistance to N. lugens, mainly due to enhanced antixenosis to female hoppers for settling and oviposition.     

Antixenosis and Antibiosis Resistance in Rice Cultivars against <Emphasis Type="Italic">Chilo suppressalis</Emphasis> (Walker) (Lepidoptera: Crambidae)

The striped stem borer, Chilo suppressalis (Walker) (Lepidoptera: Crambidae), is an important pest afflicting rice in most rice-growing countries in the world. Deliniating the categories of resistance in rice genotypes under field conditions could be helpful in managment of this pest. Two categories of resistance, antixenosis and antibiosis, were examined in ten popular and diverse rice genotypes of different origin that had been selected for their resistance to the striped stem borer in a previous study. Significant differences were found between genotypes for the number of egg masses, number of eggs, preference index, larval and pupal weight, larval development time, larval survival rate, larval mine length, and leaf trichome density. It was found that the rice genotypes Novator, A7801, and Nemat had the more pronounced antixenosis-type resistance, whereas AB1 and Shirodi had better antiobiosis-type resistance. Interestingly, the rice genotype AN-74 for which Nemat is the parental line showed both types of resistance and could be effectively used in an integrated pest management of the rice striped stem borer.     

几个粳稻品种抗白背飞虱的研究

本研究用苗期群体鉴定法对若干水稻品种进行了抗白背飞虱(Sogatella furcifera)比较测定,并探讨籼、粳稻品种抗性差异和粳稻抗性性质.结果指出:在供试“80079”,“中国91”、“盐粳2号”等粳稻品种上,白背飞虱生物学表现明显不同.粳稻抗性可分两类:(1)“80079”对白背飞虱取食、生存、发育没有抗生作用,对种群为害还表现有耐虫性;(2)“中国91”、“盐粳2号”对白背飞虱取食、生存、发育没有抗生作用,但却有一定的拒产卵机制,对种群为害还兼有耐虫性,从而能有效地抑制白背飞虱种群的建立.     

Assessing Common Bean Cultivars for Resistance to the Soybean Looper <Emphasis Type="Italic">Chrysodeixis includens</Emphasis> (Lepidoptera: Noctuidae)

The soybean looper Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae) is known as an important pest of leguminous plants worldwide. In Brazil, this pest species is gaining importance to producers of the common bean Phaseolus vulgaris L. (Fabaceae) because it limits field production of the crop. Chemical control is still the primary method of insect control. However, due to the possible harmful effects of pesticides to humans and the environment, alternative and less aggressive practices are being investigated. For this reason, the use of resistant plant genotypes represents a valuable tool in insect control. This study evaluated the biological aspects of larvae of C. includens confined to 14 bean genotypes under laboratory conditions (26 ± 2°C; 65 ± 10% RH; photoperiod of 14 h L:10 h D). The duration of the instars, total duration of the larval phase, consumption while in the larval phase, weight of the fifth instar larvae, larval viability, duration of the pre-pupal and pupal phases, pupal weight, pupal viability, pupal deformity, caterpillar-to-adult cycle, duration of the pre-oviposition and oviposition periods, and total number of viable eggs per female were evaluated. The genotypes “IAC Boreal,” “IAC Harmonia,” and “IAC Formoso” expressed antibiosis, prolonging the caterpillar-to-adult cycle and reducing the larval viability; however, each of these genotypes also experienced high leaf consumption. “IAC Jabola” expressed moderate levels of antibiosis and/or antixenosis (feeding), while the genotype “BRS Horizonte” expressed antixenosis (feeding). The data obtained with IAC Boreal, IAC Harmonia, IAC Formoso, IAC Jabola, and BRS Horizonte are promising and may help with the improvement of programs aimed at managing C. includens damage to this leguminous agricultural crop.     

Resistance of cotton genotypes with different leaf colour and trichome density to Bemisia tabaci biotype B

The silverleaf whitefly (SLW), Bemisia tabaci biotype B, is considered one of the most serious pests in cotton worldwide. Its control is based on the use of pesticides, which are well‐known for their harmful effects on non‐target organisms and the environment. Here, we examined resistance of several cotton genotypes in terms of antixenosis and antibiosis against SLW. We also investigated the mechanisms of cotton genotypes involved in antixenosis against SLW by correlating with leaf trichome density and leaf colour parameters. In choice tests, we selected resistant cotton genotypes, Gossypium hirsutum palmeri, Aubum 56‐7, G. hirsutum morrilli, Mocó, Nu‐16 (B2 B3 B6)‐ 78/658, Paymaster 53‐816 and ‘IAC 23’, based on SLW oviposition and host preference. No‐choice tests with these genotypes confirmed antixenosis effect on SLW; however, no antibiosis resistance was detected in terms of developmental period and adult emergence rate. We found SLW oviposition preference was positively correlated with trichome density in the abaxial leaf surface, while adult host preference was mostly explained by high levels of green intensity of adaxial surface. Nevertheless, both SLW oviposition and host preference were negatively correlated with the lightness level of adaxial leaf surface. Probably, the underlying mechanism of cotton resistance is based on more than just these two parameters, but our study will contribute to selecting resistant cotton genotypes and helps to understand the mechanisms involved in cotton resistance against SLW. To our best knowledge, this is the first work showing that cotton leaf colour parameters are related to resistance against SLW.     

辽宁水稻品种抗灰飞虱鉴定及其抗性机制研究

为探明辽宁地区水稻品种对本地灰飞虱Laodelphax striatellus(Fallén)的抗性水平及其抗虫机制,本研究利用改进的苗期集团鉴定法,以IR36为抗虫对照品种、武育粳3号为感虫对照品种,对42份辽宁地区主栽水稻品种和研究待推广品种进行了水稻苗期对灰飞虱抗性鉴定,并从中选取20份不同抗性水平的品种进行了排趋性和抗生性的测定。结果表明:从42份水稻材料中仅筛选出1份抗虫材料辽优5218,中抗品种11份,其余均为感虫或高感品种。在不同水稻类型中,杂交稻的抗虫性普遍较常规稻强,而从水稻株型上看,抗性品种大多为披散型。抗虫机制研究发现,抗虫品种辽优5218和中抗品种港育129兼具排趋性和抗生性,是非常理想的抗性种质资源,中抗品种港源8号和粳优558具有很强的排趋性,也是较为理想的抗性资源,为抗性机制的深入研究提供了材料。但大部分省内主栽主推品种不具备对灰飞虱的抗性,应引起重视。     

Antixenosis in maize reduces feeding by western corn rootworm larvae (Coleoptera: Chrysomelidae)

SUM2162 is the first known example of a naturally occurring maize, Zea mays L., genotype with antixenosis (nonpreference) resistance to western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), larval feeding. Behavioral responses of neonate western corn rootworm larvae were evaluated in laboratory bioassays with seven maize genotypes selected for native resistance to rootworm feeding damage. Two susceptible maize genotypes and one transgenic (Bacillus thuringiensis) maize genotype were included as controls. In soil bioassays with cut roots, no larvae entered the roots of the resistant variety SUM2162, but at least 75% of the larvae entered the roots of every other maize type. Larvae made significantly fewer feeding holes in the roots of SUM2162 than in all the other maize genotypes, except the isoline control. In feeding bioassays, larval feeding varied significantly among maize genotypes, but there was no significant difference between the resistant varieties and the susceptible controls. There were no significant differences among any of the genotypes in host recognition (search) behavior of larvae after exposure to the roots. Little variation in feeding stimulant blends was observed among maize genotypes, indicating minimal contribution to the observed antixenosis.     

Incorporation of Novel <Emphasis Type="Italic">Ceutorhynchus obstrictus</Emphasis>-resistant Canola Genotypes Into Mixed Cropping Strategies: Evidence for Associational Resistance

Canola genotypes resistant to the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), have recently been developed through introgression of Sinapis alba L. to Brassica napus L. Several lines express antixenosis and antibiosis resistance and have been shown to be less attractive to weevils in visual and olfactory behavioral bioassays. This paper details a small-plot study that assessed the effects on distribution dynamics of weevil adults and larvae of interspersing susceptible among resistant genotypes relative to monocultures over two growing seasons. Results indicate that mixes reduced weevil numbers and oviposition in pods of susceptible genotypes. These results are consistent with associational resistance.     

Hypersensitive response of beans to Apion godmani (Coleoptera: Curculionidae)

High levels of resistance to Apion godinani Wagner have been reported in bean, Phaseolus vulgaris L., landraces from Mexico. We report on the role of hypersensitivity to A. godmani in five resistant and three susceptible bean genotypes. In susceptible genotypes (cultivars 'Canario 107','Jamapa', and 'Zacatecas 45'), the eggs and first instars of A. godmani were embedded in the pod mesocarp and usually were surrounded by healthy tissue. In contrast, in resistant landraces ('Amarillo 154', 'Amarillo 155', 'J-117', 'Puebla 36', and 'Pinto 168'), necrotic tissues developed concentrically around the oviposition site, encapsulating eggs and dead larvae. An inverse relationship between percentage egg and larval encapsulation at the early immature pod stages and percentage of damaged seeds at harvest was found. Results indicate that hypersensitivity in developing pods plays an important role in antibiosis to A. godmani in beans. This information will facilitate future genetic and biochemical research and provide much needed information concerning the phenotypic basis of resistance to A. godmani in bean.     

Characterisation of bird cherry-oat aphid (Rhopalosiphum padi L.) behaviour and aphid host preference in relation to partially resistant and susceptible wheat landraces

The bird cherry-oat aphid (Rhopalosiphum padi L.) is a major pest of wheat (Triticum aestivum L.) and can cause up to 30% yield losses. Heritable plant resistance to aphids is both an economically and ecologically sound method for managing aphids. Here we report how the behaviour and performance of R. padi differs on two resistant, one susceptible wheat landrace and a susceptible elite wheat variety. Feeding behaviour differed among the genotypes, with aphids on resistant lines spending longer in the pathway phase and less time phloem feeding. These behaviours suggest that both inter- and intracellular factors encountered during pathway and phloem feeding phases could be linked to the observed aphid resistance. Locomotion and antennal positioning choice tests also revealed a clear preference for susceptible lines. Although feeding studies revealed differences in the first probe indicating that the resistance factors might also be located in the peripheral layers of the plant tissue, scanning electron microscopy revealed no difference in trichrome length and density on the surface of leaves. Aphids are phloem feeders and limiting the nutrient uptake by the aphids may negatively affect their growth and development as shown here in lower weight and survival of nymphs on resistant genotypes and decreased reproductive potential, with lowest mean numbers of nymphs produced by aphids on W064 (54.8) compared to Solstice (71.9). The results indicate that resistant lines markedly alter the behaviour, reproduction and development potential of R. padi and possess both antixenosis and antibiosis type of resistance.