Field Resistant Cultivars Research Articles

Identification of Major Quantitative Trait Loci Controlling Field Resistance to Downy Mildew in Cultivated Lettuce (Lactuca sativa).

Lettuce downy mildew, caused by Bremia lactucae Regel, is the most economically important foliar disease of lettuce (Lactuca sativa L.). The deployment of resistant cultivars carrying dominant resistance genes (Dm genes) plays a crucial role in integrated downy mildew disease management; however, high variability in pathogen populations leads to the defeat of plant resistance conferred by Dm genes. Some lettuce cultivars exhibit field resistance that is only manifested in adult plants. Two populations of recombinant inbred lines (RILs), originating from crosses between the field resistant cultivars Grand Rapids and Iceberg and susceptible cultivars Salinas and PI491224, were evaluated for downy mildew resistance under field conditions. In all, 160 RILs from the Iceberg × PI491224 and 88 RILs from the Grand Rapids × Salinas populations were genotyped using genotyping by sequencing, which generated 906 and 746 high-quality markers, respectively, that were used for quantitative trait locus (QTL) analysis. We found a QTL in chromosome 4 that is present in both Grand Rapids × Salinas and Iceberg × PI491224 populations that has a major effect on field resistance. We also found two additional significant QTLs in chromosomes 2 and 5 in the Iceberg × PI491224 RIL population. Marker-assisted gene pyramiding of multiple Dm genes in combination with QTLs for field resistance provide the opportunity to develop cultivars with more durable resistance to B. lactucae.

Effects of new field resistant cultivars and in-furrow applications of phorate insecticide on tomato spotted wilt of peanut

Field experiments were conducted at Tifton, Georgia from 2008 to 2014 to determine the effects of new peanut (Arachis hypogaea) cultivars and in-furrow applications of phorate insecticide on severity of tomato spotted wilt (TSW) caused by Tomato spotted wilt virus. Several cultivars, including Florida-07, Georgia-06G, Georgia-07W, Georgia Greener, and Tifguard, had final incidence of TSW that were less than that of Georgia Green. In-furrow applications of phorate insecticide reduced incidence of TSW in Georgia Green in three experiments in which that cultivar was included. In-furrow application of phorate insecticide reduced incidence of TSW in most cases where incidence in nontreated plots was 10% or higher. Cultivars Georganic, and Georgia-10T, had final incidence of TSW that was lower than that of Georgia-06G, or Florida-07 within nontreated plots across 2011–2012. Georgia-10T and Georgia-12Y had final incidence that was lower than that of Georgia-06G, Georgia-07W, Georgia-09B and Georgia Greener across insecticide treatments in 2013. In-furrow application of phorate increased yields across cultivars in 2008–2009, and increased yield of Georgia-09B in 2010. In most other cases, phorate had no significant effect on yield. With higher levels of field resistance in most of these cultivars, especially those such as Georgia-12Y, benefits from use of phorate insecticide for TSW suppression were small, and typically did not result in yield increase. Based on these results, several of these cultivars should allow greater flexibility for insecticide choice for thrips management without increasing the risk of losses to TSW.

CYCLOPHILIN: A DOWNY MILDEW RESISTANCE GENE CANDIDATE IN GRAPEVINE

Plasmopara viticola is the pathogen responsible for one of the most important diseases in viticulture. Vitis vinifera cultivars show almost no resistance to this pathogen except some new cultivars like ?Regent?, which achieved resistance through introgression. The molecular mechanisms of resistance are still unknown. A cyclophilin cDNA, denoted as VviCyP was isolated in grapevine. Real time PCR analysis was used to evaluate VviCyP mRNA accumulation at several time-points (0 h, 6 hpi, 12 hpi, 18 hpi, 24 hpi and 48 hpi) following infection. The field resistant cultivar ?Regent? accumulates more VviCyP transcripts at early time-points (0 h, 6 hpi and 12 hpi) whereas the sensitive cultivar ?Trincadeira? only accumulates it after the 18 hpi time-point. These results suggest that VviCyP may play an important role in the ?Regent? defence mechanism and that ?Regent? resistance capabilities are probably due to a faster perception and activation of the defence mechanism upon infection with the downy mildew pathogen.

Inheritance of field resistance to Septoria tritici blotch in the wheat doubled-haploid population Solitär × Mazurka

Breeding for field resistance to Septoria tritici blotch (STB), caused by Mycosphaerella graminicola (anamorph: Septoria tritici), is the most suitable strategy for controlling this important disease of wheat. Although many Stb genes for resistance to single pathogen isolates have been identified in wheat, knowledge of their efficiency against natural fungal populations is lacking. In a quantitative-trait-locus (QTL) mapping approach in six environments and four locations, field resistance to STB was studied in a doubled-haploid population derived from a cross between the field-resistant cultivar Solitar and the susceptible cultivar Mazurka. After plant height as a disease escape trait was accounted for, five QTL with effects on STB response on chromosomes 5A, 6D and 7D explained 20 % of the genotypic variance; QTL × environment interactions were minor. Field resistance was conferred exclusively by alleles from Solitar, which was previously shown to carry the isolate-specific genes Stb6 and Stb11 as well as minor QTL detected with seven fungal isolates. Surprisingly, neither the Stb6 nor Stb11 isolate-specific genes nor minor QTL previously detected in Solitar were found to be involved in its field resistance. The study suggests that resistance breeding for STB should not rest solely on the deployment of Stb genes. Field tests are indispensable to show their efficacy and durability and to identify genes conferring partial field resistance to STB.

Stability Analysis of Incidence of Tomato Spotted Wilt in Virginia-Type Peanut Cultivars and Breeding Lines

ABSTRACT Tomato spotted wilt (TSW) caused by Tomato spotted wilt tospovirus (TSWV) has become a serious constraint to peanut (Arachis hypogaea L.) production in the Virginia-Carolina production area. Regression stability analysis was applied to TSW incidence data collected in 64 trials conducted over 17 years to determine if an array of 31 virginia-type cultivars and breeding lines exhibited variation in their reactions to increasing levels of general TSW intensity compared with the standard field-resistant cultivar Georgia Green and hirsuta-type line PI 576636. Eight cultivars (NC 7, NC 9, NC 10C, NC-V 11, NC 12C, Perry, Phillips, and Brantley) had mean effects greater than zero (P<0.01) while Bailey, four Bailey siblings, and N96076L, Bailey's resistant parent, all had mean effects less than zero (P<0.01). The deviations of the slope of regression on environmental index (β̂k) for four of the eight susceptible cultivars were greater than zero, indicating greater than average reaction to increased levels of TSW. The β̂k for Bailey indicated that its response to increasing levels of TSW was flat. PI 576636 was confirmed as a highly field-resistant line. The slopes of Georgia Green, the standard TSWV-resistant runner-type cultivar, the Bailey siblings and N96076L did not differ from the average of all lines. The correlation between mean effect and β̂k was r = 0.693, indicating that approximately half the variation in β̂k could be explained by mean effects. However, the regression analysis provided information useful in describing the TSW reactions of the lines and cultivars.

Expression Analysis of Defense-Related Genes in Cotton (Gossypium hirsutum) after Fusarium oxysporum f. sp. vasinfectum Infection and Following Chemical Elicitation using a Salicylic Acid Analog and Methyl Jasmonate

Cotton (Gossypium hirsutum) wilt caused by Fusarium oxysporum f. sp. vasinfectum (Fov) is considered as a major threat for commercial cotton production worldwide. Relative expression ratios of two key pathogenesis-related (PR) genes (PR-3 and PR-10) and a detoxification gene (GST18) were compared between a fully susceptible (“LACTA”) and a partially field-resistant (“EMERALD”) cultivar after challenging with an Australian Fov isolate, as well as after pre-treatments with chemical inducers of defense such as BION® (a chemical analog of salicylic acid) and methyl-jasmonate (MeJA) prior to Fov inoculation. It was demonstrated that in both hypocotyls and roots of “EMERALD”, all PR genes were over-expressed after inoculation with Fov but not in the fully susceptible cultivar. Fov inoculation did not significantly affect GST18 expression in both cultivars. Exogenous application of each defense elicitor, prior to Fov inoculation, resulted in up-regulation of the three genes in root tissues of the fully susceptible cultivar. BION® application did not influence PR-3 expression in hypocotyls of both cultivars, whereas MeJA application resulted in induction of PR-3 in both cultivars. Furthermore, in hypocotyls of “LACTA”, over-expression of PR-10 was recorded after treatment with each chemical inducer. This pathogen exhibited different ability in eliciting oxidative burst in roots of the two cotton cultivars used in our analysis.

The genetic architecture of seedling resistance to Septoria tritici blotch in the winter wheat doubled-haploid population Solitär × Mazurka

Breeding for resistance to Septoria tritici blotch (STB), caused by Mycosphaerella graminicola (anamorph: Septoria tritici), is an essential component in controlling this important foliar disease of wheat. Inheritance of seedling resistance to seven worldwide pathogen isolates has been studied in a doubled-haploid (DH) population derived from a cross between the field resistant cultivar Solitar and the susceptible cultivar Mazurka. Multiple quantitative trait locus (QTL) mapping revealed major and minor genetic effects on resistance as well as several epistatic relationships in the seedling stage. Solitar conferred resistance to isolate IPO323, governed by Stb6 on chromosome 3A, as well as to IPO99015, IPO92034, Hu1 and Hu2 controlled by a QTL on chromosome arm 1BS, possibly corresponding to Stb11 and minor QTL on chromosomes 1B, 3D, 6B and 7D. Resistance of Mazurka to IPO90015 and BBA22 was caused by a QTL located in a region on 4AL which harbours Stb7 or Stb12. QTL specific to pycnidial coverage on 3B and specific to necrosis on 1A could be discovered for isolate IPO92034. Pairwise epistatic interactions were reliably detected with five isolates. Although their contributions to the total variance are generally low, the genotypic effect of the QTL by QTL interaction of 4AL (Stb7 or Stb12) and 3AS (Stb6) made up almost 15% of disease expression. Altogether, the results suggest a complex inheritance of resistance to STB in the seedling stage in terms of isolate-specificity and resistance mechanisms, which have implications for marker-assisted breeding in an attempt to pyramid STB resistance genes.

Interactive Effects of Planting Date and Cultivar on Tomato Spotted Wilt of Peanut.

Field experiments were conducted at Gainesville and Marianna, FL in 2004 and 2005 in which severity of spotted wilt, caused by Tomato spotted wilt virus, and pod yield were compared in six peanut (Arachis hypogaea) cultivars. The six cultivars included the moderately field resistant cultivars ANorden, C-99R, and Georgia Green; the highly field resistant cultivars AP-3 and DP-1; and the susceptible cultivar SunOleic 97R. There were four trials at each location, with four planting dates that ranged from late March to early June. Tomato spotted wilt severity in moderately resistant and susceptible cultivars was lower at Gainesville than at Marianna in both years in moderately resistant and susceptible cultivars. Trends in incidence for the two locations were less evident for AP-3 and DP-1. At Gainesville, there were few differences in tomato spotted wilt severity, and severity ratings were similar for Georgia Green and SunOleic 97R in two of four trials in 2004 and across all trials in 2005. At Marianna, severity ratings were lower for Georgia Green than for SunOleic 97R in six of the eight trials, and severity of tomato spotted wilt was lower for AP-3, C-99R, and DP-1 than for Georgia Green in all eight trials. In 2004, there was a trend toward decreasing severity ratings for Georgia Green and SunOleic 97R with later planting dates, but not for AP-3 or DP-1 at Marianna. Split-plot field experiments were also conducted at Tifton, GA in 2005 through 2007 in which incidence of tomato spotted wilt and pod yield were compared for peanut cultivars AP-3 and Georgia Green across planting dates ranging from late April through late May. Incidence of tomato spotted wilt was lower for AP-3 than for Georgia Green within each planting date of all years, and planting date effects were smaller in AP-3, if observed at all, than in Georgia Green. In most planting dates of all three trials, yields were higher for AP-3 than for Georgia Green. The relationships between yield and planting date were not consistent. These results indicate that the level of field resistance in AP-3 and DP-1 cultivars is sufficient to allow planting in late April without greatly increasing the risk of losses to tomato spotted wilt.

Some spatial, temporal and spatio-temporal considerations of wood decay of tea ( Camellia sinensis), caused by Nemania diffusa (Syn. Hypoxylon vestitum)

Tea stem wood decay caused by N. diffusa is confirmed here to be a soft rot. The activity of periodic pruning of tea bushes contributed to dissemination of disease through the contaminated pruning knife. Once contaminated, the infection can spread linearly in either direction at approximately 1.2 cm per annum. This compared well with the rates experienced under ex situ inoculation tests, which worked out to be 1.7 cm per annum. Field resistant tea cultivars recorded a relatively lower number of fibre cells than the field susceptible cultivars. The natural susceptibility (decay potential) of tea stem wood due to N. diffusa infection was around 69 g cm −3 yr −1, with the capacity to cause in vitro wood loss/decay in the range of 62–75%. Under natural field conditions, long-term infections accounted for an increase in disease score of about 0.3 for every 1 m rise in altitude starting from a base level of 1500 m, commensurate with a rate of increase of disease of approximately 0.01% m −1 rise per year.

Response of Peanut, Pepper, Tobacco, and Tomato Cultivars to Two Biologically Distinct Isolates of Tomato spotted wilt virus.

Spotted wilt disease, caused by Tomato spotted wilt virus (TSWV), is an economically important disease in peanut, pepper, tobacco, and tomato in the southeastern United States. However, very little is known about the biological variability existent in the virus population. Fourteen isolates of TSWV collected in Georgia were evaluated for symptom severity. The majority of the isolates produced severe systemic necrosis. One mild (GATb-1) and one severe (GAL) isolate were further examined because of the distinct differences in their virulence and symptomatology on tobacco. GATb-1 caused a few chlorotic spots and mild systemic symptoms, whereas GAL produced a large number of local lesions and severe systemic necrosis. Distinct differences in the response of selected commercial cultivars of peanut, tobacco, and tomato to GATb-1 and GAL infection were observed. GAL was lethal to a widely grown tobacco cultivar, K326. Georgia Green, a field resistant peanut cultivar, and C11-2-39, a breeding line with the highest level of known resistance to TSWV, were more susceptible to GAL than to GATb-1. BHN 444, a newly released TSWV-resistant tomato cultivar, showed a resistant reaction, whereas Stiletto, a newly released TSWV-resistant pepper cultivar, was susceptible to both GATb-1 and GAL isolates. Information on the biological diversity of TSWV may be useful in developing more durable TSWV-resistant crops.

Methyl jasmonate induced gene expression in wheat delays symptom development by the crown rot pathogen Fusarium pseudograminearum

The necrotrophic fungal pathogen Fusarium pseudograminearum ( F. pseudograminearum) causes crown rot disease (CR) in wheat. This host–pathogen interaction has not been studied previously at the molecular level. In this study, using real-time quantitative PCR, the expression of 26 selected wheat genes was examined 1, 2 and 4 days after inoculation of wheat seedlings of the CR susceptible cultivar Kennedy and the partially field-resistant cultivar Sunco. Reproducible induction of eight defence genes consisting of PR1.1, PR2 ( β, 1‐ 3 glucanase), PR3 ( chitinase), PR4 ( wheatwin), PR5 ( thaumatin-like protein), TaPERO ( peroxidase), PR10 and TaGLP2a ( germin-like) was observed. These genes were induced in both cultivars, however, some genes were induced more rapidly in Sunco than in Kennedy. MJ treatment also induced the above pathogen responsive defence genes in both cultivars while benzo(1,2,3)thiadiazole-7-carbothionic acid S-methyl ester (BTH) treatment weakly induced them in Kennedy only. Similarly, treatment with MJ before inoculation significantly delayed the development of necrotic symptoms for 2 weeks in both wheat cultivars, while BTH pre-treatments delayed symptom development in Kennedy only. The chemically induced protection, therefore, correlated with induction of the F. pseudograminearum-responsive genes. These results support the emerging role of jasmonate signalling in defence against necrotrophic fungal pathogens in monocots and future manipulation of this pathway may improve CR resistance in wheat.

Susceptibility of potato (Solanum tuberosum) cultivars to powdery scab (caused by Spongospora subterranea f. sp. subterranea), and relationships between tuber and root infection

Ninety-nine potato (Solanum tuberosum) cultivars and 13 breeding lines were assessed in field trials for susceptibility to powdery scab (caused by Spongospora subterranea f. sp. subterranea). The trials wer e carried out over 11 growing seasons (each cultivar/line tested in at least two growing seasons) in soil inoculated with S. subterranea and regularly irrigated during crop growth. The cultivars and lines were categorised as ‘very resistant’ (21%). ‘moderately resistant’ (28%). ‘moderately susceptible’ (33%) or ‘very susceptible’ ( 19%). Scaled average severity scores for the cultivars and lines followed a continuum between very resistant and very susceptible, suggesting that resistance to powdery scab is quantitative. In a glasshouse experiment where small plants were inoculated with S. subterranea sporosori, 15 cultivars selected to cover the spectrum of field-assessed susceptibility were assessed for intensity of infection by S. subterranea zoosporangium in roots and for numbers of root galls on root systems. All of the cultivars developed zoosporangia and root galls (i.e. no cultivar was immune from infection), and root infection was usually related to tuber infection. Field-resistant cultivars (tuber infection) generally had low numbers of root zoosporangia and root galls in the glass house experiment, and cultivars that were very susceptible to tuber infection in the field had high levels of root infection in the glasshouse experiment. An exception was the early maturing cv. Swift, which had very low levels of tuber infection in the field, but had high numbers of root zoosporangia and root galls in the glasshouse. These results demonstrate the relative reaction of a large number of potato cultivars to powdery scab and reaffirm the potential for using plant resistance as a powdery scab management strategy. Development of S. subterranea in host roots, even in cultivars with resistance to tuber infection, is likely to be important in the epidemiology of powdery scab.

Response of Hard Red Winter Wheat to Soilborne wheat mosaic virus Using Novel Inoculation Methods

ABSTRACT Soilborne wheat mosaic virus (SBWMV) is an agronomically important pathogen of wheat that is transmitted by the soilborne plasmodiophorid vector Polymyxa graminis. In the laboratory, attempts to generate SBWMV-infected plants are often hampered by poor infectivity of the virus. To analyze the mechanism for virus resistance in wheat cultivars, we developed novel inoculation techniques. A new technique for foliar inoculation of SBWMV was developed that eliminated wound-induced necrosis normally associated with rub inoculating virus to wheat leaves. This new technique is important because we can now uniformly inoculate plants in the laboratory for studies of host resistance mechanisms in the inoculated leaf. Additionally, wheat plants were grown hydroponically in seed germination pouches and their roots were inoculated with SBWMV either by placing P. graminis-infested root material in the pouch or by mechanically inoculating the roots with purified virus. The susceptibility of one SBWMV susceptible and three field resistant wheat cultivars were analyzed following inoculation of plants using these novel inoculation techniques or the conventional inoculation technique of growing plants in P. graminis-infested soil. The results presented in this study suggest that virus resistance in wheat likely functions in the roots to block virus infection.

Sources of Resistance to Eastern Filbert Blight in Hazelnut

Eastern filbert blight is an economically significant disease in European hazelnut (Corylus avellana L.) production in the United States. Since genetic resistance is the only viable disease control strategy to this fungal disease caused by Anisogramma anomala (Peck) E. Müller, greenhouse and field screening of germplasm was undertaken to study the inheritance from known resistant sources and to identify new sources for inclusion in the breeding program. We confirmed that `Gasaway' resistance to this disease is conferred by a single dominant gene. No major gen was identified in the field-resistant cultivar Gem. Representatives of six Corylus species were screened to identify new resistant germplasm. Corylus cornuta Marshall var. cornuta, C. cornuta var. californica (A.DC.) Sharp, C. heterophylla Fischer, and C. sieboldiana Blume were highly resistant, as were most C. americana Marshall genotypes and one C. colurna L. clone tested, but C. jacquenontii Decaisne was highly susceptible. In several cases, hybrids of these species with susceptible C. avellana were also resistant. These new sources of resisstance are being incorporated in the resistance breeding effort.

Rate‐Reducing Resistance to Fusarium solani f. sp. phaseoli underlies Field Resistance to Soybean Sudden Death Syndrome

Yield losses occur in soybean [Glycine max (L.) Merr.] because of sudden death syndrome (SDS) caused by Fusarium solani (Mart.) Saec. f. sp. phaseoli (Burk.) Snyd. & Hans, type A. Our objective was to determine whether tolerance or partial resistance to infection underlies field resistance to SDS. Seven field resistant cultivars and five susceptible cultivars were planted at two locations. Twenty taproots per cultivar were sampled every 7 to 21 d from the V0 to R8 growth stages, 8 to 121 days after planting (DAP). Six taproot sections per plant were tested for F. solani on a selective medium. Infection frequency (IF), the percentage of infected plants, and infection severity (IS), the percentage of infected root segments, were scored. Leaf symptoms were recorded and standardized to the R6 stage and the disease index (DX) was calculated. Infection was detected at the VI stage (within 15 DAP) and reached a maximum by about R1 (55–68 DAP). All cultivars were infected by F. solani. However, seasonal mean IF and mean IS were significantly lower among the resistant cultivar class. After R1, infection was also significantly lower among the resistant cultivar class within individual sampling dates. Also, DX and IF were correlated in each environment (r = 0.38 and 0.61). Therefore, in the resistant cultivars Forrest, Ripley, Jack, PI520733, ExF44, ExF59, and ExF78, late season rate‐reducing (partial) resistance decreased the DX, IF, and IS. Resistance probably extends the latent period of F. solani. Among susceptible cultivars, Essex and A5403, had reduced leaf symptoms but high IF and IS suggesting tolerance to F.solani that alleviated SDS.

An Association Between High Peroxidase Activity in Lettuce (Lactuca sativa) and Field Resistance to Downy Mildew (Bremia lactucae)

AbstractThe association between variation for pre‐infection peroxidase activity and levels of field resistance‐susceptibility to downy mildew (Bremia lactucae) was investigated in lettuce (Lactuca sativa) cultivars, accessions of L. serriola (prickly lettuce), segregating F2 populations and selected F3 families from a cross between field resistant and susceptible lettuce cultivars. A trend was apparent in this series of experiments indicating that one component of field resistance could be related to a high level of peroxidase activity prior to infection. The data suggest that in breeding programmes there could be merit in imposing primary selection for high peroxidase activity prior to field selection for resistance.

The involvement of mechanical barriers in the resistance response of a field-resistant and a field-susceptible potato cultivar to Verticillium dahliae

The association of phytotoxin production by the pathogen Verticillium dahliae with the production of wilt symptoms in susceptible potato cultivars has been well documented. However, certain cultivars exhibit field resistance although isolated tissues and cell cultures of these cultivars demonstrate susceptible responses when treated with phytotoxins from V. dahliae. Therefore more than one type of resistance, other than biochemical insensitivity to phytotoxins such as hypersensitivity and mechanical barriers, may be present. We investigated several defence mechanisms, including hypersensitivity, suberization, wound periderm formation and phytoalexin production in tubers of a field-susceptible (Kennebec) and a field-resistant (Reddale) cultivar, both of which are sensitive to V. dahliae phytotoxins. Although the total number of suberized cell layers and wound periderm formed were not different between the two cultivars, the response was more rapid in the resistant cultivar. Tuber tissue discs of the resistant cultivar exhibited more rapid and intense hypersensitive browning than the susceptible cultivar when inoculated with V. dahliae, whereas treatment with the elicitor arachidonic acid produced similar responses in both cultivars. High levels of the phytoalexin rishitin where produced in the susceptible cultivar when inoculated with the fungus, but only trace levels of rishitin were found in the resistant cultivar regardless of treatment. These results indicate that rapid mechanical defensive mechanisms play an important role in the resistance of potato cultivars to seed-piece infection by V. dahliae, while in the cultivars studied the production of phytoalexins is not correlated with resistance.

Identification of field resistant rice cultivars for tungro disease

Abstract Two hundred and one rice cultivars bred at Central Rice Research Institute (CRRI) were evaluated for tungro resistance by field screening technique. Fourteen rice cultivars were identified as field resistant. Based on field evaluation trial and greenhouse reaction, the rice cultivars CR146–7003, CR 260–131–5–713, CR 260–136–321 and CR 319–644 had high degree of resistance to tungro with high yielding ability. These cultivars are being tested in multi‐locational trials for their suitability under different agroclimatic conditions in various parts of India. Eighteen hundred cultivars bred by breeders in different states of India were field evaluated for tungro resistance. Nine cultivars were rated as highly resistant to tungro under field conditions. Out of 70 multiple resistant varieties tested, a bacterial leaf blight resistant variety BJ 1 had a high degree of resistance to tungro also.

Genetics of Field Resistance of Rice to Brown Planthopper1

The brown planthopper [Nilaparvata lugens (Stal)] is one of the most serious insect pests of rice (Oryza sativa L.) in South and Southeast Asia. Because cultivars with vertical resistance to brown planthopper have “broken down” due to brown planthopper biotype selection, field resistant cultivars with horizontal resistance are being evaluated. The inheritance of field resistance to brown planthopper in two traditional rice cultivars, ‘Utri Rajapan’ and ‘Triveni’, was investigated. Twenty‐day old seedlings were infested with second and third‐instar brown planthopper nymphs. Reactions of F1, F2, and F3 populations from the crosses of resistant cultivars with the susceptible parent ‘TN1’ revealed that two independently segregating recessive genes govern resistance in both cultivars. Allelism tests revealed that the two cultivars have the same genes for resistance.

Greenhouse techniques to identify field resistance to the brown planthopper, Nilaparvata lugens (Stål) (Homoptera: Delphacidae), in rice cultivars

Two seedbox screening techniques were compared to determine levels of resistance of rice cultivars to three brown planthopper, Nilaparvata lugens (Stål), biotypes. The commonly used standard seedbox screening test (SSST) where eight second-instar nymphs were infested on 7-day-old seedlings was compared with a modification (MSST) where four second-instar nymphs were infested on each of 20-day-old plants. In the SSST, the initial infestation killed the susceptible cultivars whereas in the MSST the F 1 progeny killed the susceptible cultivars. The cultivars ASD 11, Wagwag, Utri Rajapan, IR46 and Kencana were susceptible in the SSST but moderately resistant or resistant in the MSST, indicating an increase in the level of resistance with plant age. Feeding rate and population growth of N. lugens were the factors involved in the resistance of 30-day-old plants. The MSST provides a rapid method for identifying field-resistant cultivars in the greenhouse and can be used to identify field-resistant lines in a rice-breeding programme for stable resistance to N. lugens.