Variation in performance of western flower thrips populations on a susceptible and a partially resistant chrysanthemum cultivar

Variation in host plant performance among populations of a phytophagous insect pest is a potential threat to the durability of host plant resistance. Aggressive biotypes may overcome the protective properties of formerly resistant cultivars. Therefore, it is of interest to study such variation in breeding programs for host plant resistance to insects. In the present study, the performance of ten populations of Frankliniella occidentalis, the western flower thrips, was determined on a susceptible and a partially resistant cultivar of chrysanthemum, Dendranthema grandiflora. Damage, reproduction, and adult survival were determined using an excised leaf assay. Significant differences between the two cultivars and among the ten populations were found for all three characteristics. In general, damage, reproduction and adult survival were reduced on the resistant cultivar when compared to the susceptible cultivar. Some populations showed, in comparison to the reference population from the Netherlands, much higher damage and reproduction on one or both chrysanthemum cultivars. But also in these populations performance on the resistant cultivar was poor compared to the susceptible cultivar. This revised version was published online in August 2006 with corrections to the Cover Date.     

西花蓟马在低温下的生长发育和繁殖研究

为探明低温对西花蓟马[Frankliniellaoccidentalis(Pergande)]生长发育和繁殖的影响,全面了解西花蓟马的生活习性,为其综合防治提供依据。将西花蓟马分别置于5℃、10℃低温培养箱中,每天观察记录2种环境温度下西花蓟马的生长发育和繁殖情况。研究表明,5℃下西花蓟马不能完成生活史,卵不能正常孵化;1龄若虫可以发育到2龄,但2龄若虫不能继续发育至蛹;蛹能够发育至成虫但成虫不能产卵;10℃下西花蓟马能够完成生活史,但是发育历期显著延长。上述结果表明,低温导致西花蓟马的发育速度减慢,后代数量骤减,但西花蓟马转移至室温环境后,能够恢复正常生长,说明其具有很强的低温耐受性,防治中应充分注意西花蓟马的这一低温耐受特性,在早春温度回升和其种群数量开始上升时及时进行防治。     

Inheritance of resistance to damage byThrips tabaci Lindeman (Thysanoptera: Thripidae) in Cabbage

Summary The inheritance of resistance in cabbage (Brassica oleracea var.capitata) to damage caused byThrips tabaci Lindeman was studied in progeny from four crosses between resistant and susceptible inbred lines. In two families sharing the same susceptible parent, the narrow-sense heritability was calculated to be high (>90%), using the Warner method of calculation (Warner, 1952). The other two families, also sharing a susceptible parent, had very low narrow-sense heritability (0–11%). In three of the four families, however, the validity of the Warner calculations were called into question due to significant epistatic interactions. In all four families, the F₁ populations approached or exceeded the susceptibility of the susceptible parent, indicating that susceptibility is generally dominant. The importance of epistasis and dominance suggests that tests of hybrid combinations to determine combining ability for thrips resistance may be required, rather than selecting only on the basis of thrips damage to the inbred lines. The technique of planting wheat upwind from the cabbage test plot did generate adequate levels of thrips pressure, but the infestation was uneven in two of the four blocks, so that reasonable replication of tests is required.     

Detection of quantitative trait loci (QTL) associated with resistance to whitebacked planthopper (Sogatella furcifera) in rice (Oryza sativa)

Whitebacked planthopper (WBPH) is an important insect pest of rice. In this study, we report quantitative trait loci (QTL) associated with resistance to WBPH using a doubled‐haploid (DH) mapping population derived from the cross IR64/Azucena. We evaluated a set of 91 DH lines using various screening tests which measure seedling resistance, antibiosis and tolerance to WBPH. QTL analysis involving a RFLP map of 175 markers detected a significant QTL on chromosome 7 (RG511‐RG477) associated with seedling resistance to WBPH. In addition, QTL analysis involving available defence related candidate genes as markers on a sub set of 60 DH lines showed significant association of genomic regions on chromosome 1 (W1‐pMRF1), 2 (XLRfrI7‐RG157) and 7 (RG711‐CDO418) with resistance to WBPH. Several suggestive QTL were detected on chromosomes 2, 3, 6, 7, 8 and 11 showing the possibility of their association with resistance to WBPH. The phenotypic contribution of the QTL ranged from 8.4% to 32.1%. Some of the WBPH resistance QTL detected in this study showed similar map positions with the QTL reported for resistance to brown planthopper (BPH) in the same mapping population. These results would be useful for attempts to trace the genes associated with resistance to planthoppers in rice.     

Allelic variation of a clubroot resistance gene (Crr1a) in Japanese cultivars of Chinese cabbage (Brassica rapa L.)

Clubroot resistance (CR) is an important trait in Chinese cabbage breeding worldwide. Although Crr1a, the gene responsible for clubroot-resistance, has been cloned and shown to encode the NLR protein, its allelic variation and molecular function remain unknown. Here, we investigated the sequence variation and function of three Crr1a alleles cloned from six CR F₁ cultivars of Chinese cabbage. Gain-of-function analysis revealed that Crr1a^Kinami90_a isolated from the cv. ‘Kinami 90’ conferred clubroot resistance as observed for Crr1a^G004. Because two susceptible alleles commonly lacked 172 amino acids in the C-terminal region, we investigated clubroot resistance in transgenic Arabidopsis harboring the chimeric Crr1a, in which 172 amino acids of the functional alleles were fused to the susceptible alleles. The fusion of the C-terminal region to the susceptible alleles restored resistance, indicating that their susceptibility was caused by the lack of the C-terminus. We developed DNA markers to detect the two functional Crr1a alleles, and demonstrated that the functional Crr1a alleles were frequently found in European fodder turnips, whereas they were rarely introduced into Japanese CR cultivars of Chinese cabbage. These results would contribute to CR breeding via marker-assisted selection and help our understanding of the molecular mechanisms underlying clubroot resistance.     

Resistance to western flower thrips in greenhouse cucumber: effect of leaf position and plant age on thrips reproduction

Three greenhouse cucumber (Cucumis sativus L.) accessions, previously selected for low levels of damage after infestation with Frankliniella occidentalis (Pergande), were tested for resistance against F. occidentalis in a no-choice greenhouse experiment at the mature plant stage. The three accessions showed a strong reduction in thrips damage compared to the susceptible control. The effects of leaf position and plant age of the four cucumber accessions on the reproduction of F. occidentalis were determined in a leaf disc assay. Leaf position had a significant effect on thrips reproduction, whereas plant age, within the test range, had not. In general, reproduction was higher on young leaves. Reproduction as measured on leaf discs from certain leaf positions was strongly correlated with resistance of mature plants in the greenhouse, and can therefore be used as a quick test to screen cucumber accessions for resistance against thrips. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic variation in testcrosses of European maize inbreds for resistance to the European corn borer and relations to line per se performance

The European com borer (ECB) Ostrinia nubilalis H. is a major pest in World maize Zea mays L. production. Objectives of this study were to (1) investigate the genotypic variance and covariance in testcrosses of European flint and dent inbreds for ECB resistance and agronomic traits, and (2) estimate the correlation between line per se and testcross performance for ECB resistance traits. A total of 16 flint and 24 dent inbreds and their testcrosses with two testers from the opposite germplasm pool were evaluated in four and three German environments, respectively. Using artificial infestation with ECB larvae, resistance was assessed by damage rating of stalks, tunnel length in dissected stalks, and relative yield of infested plots compared with protected plots. Yield losses due to ECB damage in testcross hybrids amounted to 40%. Significant genotypic variances between flint and dent lines and high heritabilities were found for damage rating of stalks for both line per se and testcross performance. Heritabilities were low or intermediate for tunnel length and relative grain yield. Correlations between line per se and testcross performance were tight for the damage rating of stalks and moderate for tunnel length and relative yield in both flint and dent germplasm. For damage rating of stalks, per se performance of lines tested in a few environments can be used to predict their testcross performance. In contrast, assessment of testcross performance for tunnel length and relative yield requires evaluating testcrosses with several testers in multi-environment trials.     

不同光质对菊花组培苗生长的影响

本文研究新型光源LED辐射的不同光质对菊花组培苗生长的影响,以期为植物组培专用LED光源的研发提供数据支持和理论依据。以菊花组培苗为试材,采用LEDs光源发射的单色光谱红光[(658±20) nm]、蓝光[(460±20) nm]、远红光[(730±20) nm]和绿光[(530±20) nm],进行不同光质配比组合,荧光灯作为对照,对组培苗形态、生根,色素含量,碳氮代谢及抗氧化酶系活性进行差异比较。菊花组培苗在红光下徒长,能效最大。蓝光下矮壮,根系活力最大,复合LEDs光质下,组培苗形态正常。RBG处理的菊花组培苗叶片色素含量最高。红光有利于叶绿素b的合成,蓝光有利于叶绿素a的合成。单频红光处理的菊花叶片淀粉含量最高,RBG处理的叶片可溶性糖、碳水化合物蔗糖、游离氨基酸含量最高。蓝光有利于蛋白质的合成,LEDs光质处理的叶片C/N比高于荧光灯。随着LEDs技术的改进与发展, LEDs光照系统将会替代荧光灯成为植物组织培养的理想光源。     

A New Source of Resistance to Puccinia striiformis f. sp. tritici in Spring Wheats (Triticum aestivum)

The use of P. striiformis f. sp. tritici pathotypes virulent or avirulent with respect to both Yr6 and a previously undescribed source of resistance, designated YrA, allowed the recognition of the corresponding host resistance genes m a range of Australian and exotic spring wheats. The phenotypes conferred by the YrA resistance varied when exposed to contrasting light intensities in the post-inoculation phase. The implications of the results in international studies of host resistance to P. striiformis f. sp. tritici are discussed.     

Field resistance of perennial glandular-haired Medicago strains and alfalfa cultivars to the alfalfa weevil

Summary Field plots planted in 1986 to four, perennial, glandular-haired Medicago strains and four alfalfa cultivars were evaluated for alfalfa weevil, [Hypera postica (Gyllenhal)], abundance and feeding damage as well as plant height from 23 April through 21 may 1987 and from 25 April through 26 May 1988. The plots were located near Mead, Nebraska and both sweep and stem sampling methods were utilized. In 1987, M. glandulosa had the fewest larvae present in sweep samples on 1, 9, and 15 May, although on the last date it did not differ significantly from three other entries. The glandular-haired M. glandulosa also was among those entries having the fewest number of larvae present in stem samples on 9 May, 1987. Significant differences in the number of damaged stem tips were observed on 9 and 21 May, 1987, when M. glandulosa was among those entries having the least amount of damage. The other three glandular-haired strains had larval infestations and damage similar to those for the cultivars. Weevil abundance and damage were generally low in 1988. Medicago glandulosa was shortest of the glandular-haired strains, which were shorter than the cultivars.     

Genetic markers linked to Striga gesnerioides resistance for the improvement of Ghanaian cowpea (Vigna unguiculata) cultivars

The parasitic plant, Striga gesnerioides (Willd.) Vatke, is one of the most important constraints of cowpea production and food security in West Africa. Currently, few Striga resistant cowpea varieties have been developed that are well‐adapted to the dry savannah regions of Ghana. While genes conferring resistance to Striga races SG1, SG3 and SG5 have been mapped, the genetic locus of resistance to the race of Striga found in Ghana (SG‐GH) has not been characterized. Here, we report identification of genetic markers linked to SG‐GH resistance and define the relationship of this locus to SG3 resistance in recombinant inbred line populations generated from crosses between Striga resistant IT97K‐499‐35 and the Striga susceptible varieties Apagbaala and SARC‐LO2. The populations were genotyped with five genetic markers associated with SG3 and SG5 Striga resistance genes and a genetic map was developed. Genes conferring resistance to SG‐GH and SG3 mapped 4.2 cM from each other on chromosome Vu11. The identification of genetic markers linked to SG‐GH resistance will facilitate the marker‐assisted development of high‐quality Striga resistant cowpea varieties in Ghana.     

A six week screening method for mechanisms of host plant resistance to Diuraphis noxia in wheat accessions

The Russian wheat aphid Diuraphis noxia (Kurdjumov) is a serious pest of wheat in South Africa. The use of D. noxia-resistant cultivars may reduce the impact of this pest on wheat production and at the same time reduce environmental risks and control costs. The mechanisms of resistance in two new sources of resistance were compared by using various methods, in order to establish a rapid and relatively accurate screening protocol. The resistant lines OSU ID 2808 and Aus 22498 were compared to the susceptible cultivars Betta and Tugela. The predominant mechanism of resistance in OSU ID 2808 was antibiosis, although a low level of antixenosis may also be present. The line Aus 22498 was primarily a tolerant type, with a moderate level of antibiosis and a low level of antixenosis. A six week screening procedure is described using the colony count technique for antibiosis, a completely random free choice experiment for antixenosis and a three week test measuring initial and final plant height, initial and final D. noxia infestation, damage rating, leaf area and dry plant mass for tolerance. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic variation and response to selection for resistance to root-knot nematodes in oil radish (Raphanus sativus ssp. oleiferus)

Based on a preliminary screening of a collection of cruciferous crops, such as oilseed rape (Brassica napus L. ssp. oleifera Metzg.), oil radish (Raphanus sativus L. ssp. oleiferus DC.), and yellow mustard (Sinapis alba L.), some plants within the oil radish varieties showed resistance to the root-knot nematodes Meloidogyne hapla Chitwood and M. incognita (Kofoid & White) Chitwood. Resistance tests of S₁ progeny of these selected genotypes revealed a quantitative nature of resistance to M. hapla. Only a few resistant individuals were found, but a significant effect of selection was observed. In contrast, the progenies of plants resistant to M. incognita showed a very low number of egg masses, suggesting that this resistance may be conferred by dominant major gene(s). The results indicate that resistance of oil radish to root-knot nematodes may be effective and may thus provide new possibilities for the management of M. hapla and M. incognita.     

Genotypic variation of resistance to the spotted stalk borer Chilo sacchariphagus (Bojer) in sugarcane: evidence of two distinct resistance mechanisms

We carried out an assessment of the resistance status to the spotted stalk borer Chilo sacchariphagus in a sample of 32 international sugarcane clones in Reunion. Our objectives were to characterize the genotypic variability of resistance and to characterize the role of leaf and stalk resistance in the global resistance. A significant genotypic variability in the % exited tunnels and in the leaf feeding injuries confirmed the existence of two resistance mechanisms located respectively in the leaves and in the stalk. Leaf resistance and stalk resistance exhibited genotypic and phenotypic correlation with stalk tunnelling injuries. No phenotypic or genotypic correlations were observed between leaf resistance and stalk resistance. Both resistances contributed independently to the global resistance quantified by the stalk tunnelling. The resistance status of the two main cultivars cultivated in Reunion was assessed within our germplasm sample: 'R 570' was one of the most resistant clones and 'R 579' proved to be moderately susceptible.     

Genetic analysis of adult plant leaf rust resistance in three bread wheat (Triticum aestivum L.) cultivars

Genetic basis of adult plant leaf rust resistance in three released Indian wheat cultivars viz. DWR195, RAJ3765 and HP1731 was investigated through detailed inheritance study under controlled polythene house condition at Flowerdale, India. The F₂, F_3, F₄ and F₅ generations were analyzed with the most frequent and virulent Indian leaf rust pathotype 121R63-1. Two complementary recessive genes imparted resistance in DWR195, two complementary dominant genes governed the resistance of RAJ3765 whereas two independent dominant genes were involved in the resistance of HP1731. The genes responsible for adult plant resistance in the three cultivars were not allelic. The two complementary genes of DWR195 and two independent dominant genes of HP1731 have been isolated as single gene lines. Utilization of resistance from HP1731, which carries two independent dominant genes, will be easy as compared to DWR195 and RAJ3765.     

Identification of high levels of resistance to cabbage root fly, Delia radicum, in wild Brassica species

Wild Brassica species and associated breeding lines were evaluated for their resistance to Delia radicum, the cabbage root fly, in the field in 1993 and in the field, glasshouse and laboratory in 1996. High levels of antibiosis resistance were discovered in the field in 1993 in Brassica fruticulosa, B. incana, B. villosa and B. spinescens and confirmed in the field in 1996 while two B. oleracea accessions and the susceptible control Brussels sprouts variety, ‘Oliver’, were highly susceptible. No D. radicum pupae were found in the soil around the roots of B. fruticulosa and B. spinescens at the end of the season. All the Brassica species were attractive to egg-laying by D. radicum in the field and in a laboratory experiment and therefore lacked antixenosis resistance. In a series of glasshouse experiments, Brassica species and breeding lines were inoculated with D. radicum eggs supplied from a laboratory culture and the effects of larval feeding on plants recorded. Brassica incana, B. fruticulosa and B. spinescens were highly resistant, most plants surviving, whilst B. macrocarpa and B. villosa were moderately resistant as were two F1 lines bred from a cross between B. macrocarpa and B. oleracea. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inheritance of resistance to whitebacked planthopper,Sogatella furcifera (Horvath) in some rice cultivars

Summary The genetics of resistance to whitebacked planthopper, Sogatella furcifera (Horvath) in ten resistant cultivars was studied. The reactions of the F₁, F₂ and F₃ populations of resistant varieties with Taichung Native 1, a suspectible check, showed that WBPH resistance is monogenic in nature and governed by dominant gene(s) in Ptb 19 and IET 6288 and recessive gene in eight cultivars viz. ARC 5838, ARC 6579, ARC 6624, ARC 10464, ACR 11321, ARC 11320, Balamawee and IR 2415-90-4-3. Allelic relationship of resistance gene(s) in the test cultivars revealed recessive gene in IR 2415-90-4-3, ARC 5838 and ARC 11324 to be allelic but it was non allelic to the resistance gene in ARC 6624. Cultivars ARC 6579, ARC 11321 and Balamawee have identical gene among themselves but their relationship with IR 2415-90-4-3, ARC 5838, ARC 11324 and ARC 6624 is unknown. The recessive gene in ARC 10464 is non-identical to all other cultivars having the recessive gene except ARC 6624 with which its relationship needs further investigation.     

Levels of host plant resistance to banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae), in African Musa germplasm

Forty-five Musa clones, including endemic and introduced cultivars plus hybrids, were evaluated for resistance against the banana weevil, Cosmopolites sordidus, in a field trial in Uganda. The predominant groups of staple crops, East African highland bananas (Musa spp. AAA) and plantains (Musaspp. AAB), as well as plantain-derived hybrids (AAB × AA), showed the highest levels of susceptibility to this pest. These were followed by dessert bananas (Musa spp. AAA), exotic bananas (Musa spp. ABB) and finally diploids of M. acuminata (AA). Hybrids of banana origin were highly resistant. Some East African highland cultivars, especially brewing types (e.g., Kabula, Bagandeseza, Ediirira), showed intermediate levels of resistance. Among the non-highland bananas, high levels of resistance were observed in Yangambi-Km5 (AAA), Cavendish (AAA), Gros Michel (AAA), Kayinja (ABB, Pisang Awak subgroup), Ndiizi (AB, Ney Poovan subgroup)and Kisubi (Ney Poovan subgroup). The highest resistance was observed in banana hybrids TMB2×7197-2, TMB2×8075-7 and the wild banana Calcutta-4 (AA). These were considered the best sources of resistance for a weevil resistance-breeding programme with the two hybrids commonly used as improved male parents. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of the durable resistance to yellow rust in old winter wheat cultivars in the Netherlands

Summary Winter wheat cultivars released in the Netherlands before 1930 carried durable resistance to yellow rust. Cultivars released in the period between 1930 and 1950 often were durably resistant while recent cultivars infrequently showed durable resistance. This durable resistance was not difficult to transfer to new cultivars. Twenty nine older cultivars with durable resistance and eight recent non-durably resistant cultivars were tested in the seedling stage and in the adult plant stage against 12 West-European yellow rust races and against some non-European races in the seedling stage only. The adult plant tests were carried out in race nursery tests in the Flevopolder. Per race nursery all 37 cultivars, planted in hills of about 20 plants on both sides of the highly susceptible cv. Michigan Amber, were exposed to one race.The infection type of each cultivar-race combination was scored on 0 to 9 scale once in the seedling stage and twice in the adult plant stage. In the race nurseries the percentage leaf area affected was evaluated three times to be used to calculate the area under the disease progress curve (AUDPC). This AUDPC multiplied with the mean infection type in the field gave the susceptibility index (SI).The infection types were classified into resistant (R), intermediate (I) or susceptible (S) when the infection types were 0 to 3, 4 to 6 or 7 to 9, respectively. Four categories of resistance were discerned on the basis of the three infection type scores: 1) RRR, overall resistance; complete or near-complete resistant at all stages. 2) SRR, adult plant resistance, complete- or near-complete resistant at the adult plant stage only. 3) SRS and SSR, temperature sensitive resistance, the resistance changed from the one evaluation data to the other. 4) SSS and an SI lower than that of Michigan Amber, partial resistance.The frequencies of overall, adult plant and temperature sensitive resistance were 1.4, 52 and 54% in the older cultivars and 40, 62 and 22% in the recent ones, respectively. Among the older cultivars all had a fair to high level of partial resistance, the SI being on average only 20% of that of Michigan Amber, while most cultivars also seemed to carry temperature sensitive resistance. The partial resistance of the recent cultivars was of a much lower level with a mean SI compared to that of Michigan Amber of 61%. Partial resistance was highly correlated (r = –0.94) with the mean resistance scores from the Dutch Recommended Cultivars Lists. It was concluded that partial resistance and temperature sensitive resistance were the major components of the durable resistance in the older cultivars.     

Evaluation of resistance of apricot cultivars to a Spanish isolate of plum pox potyvirus (PPV)

The resistance of 12 apricot cultivars to the Dideron type Spanish isolate RB3.30 of plum pox potyvirus was evaluated in controlled conditions in an insect‐proof greenhouse. The results of the evaluation demonstrated the resistance of the cultivars ‘Stella’, ‘Stark Early Orange’, ‘Goldrich’, ‘Harcot’, ‘NJA2’, ‘Pandora’ and ‘Avilara’ to the isolate, and the susceptibility of the cultivars ‘A1453’, ‘Bulida’,‘Currot’, ‘Real Fino’ and ‘Canino’