Diversity of white and narrow-leafed lupin genotype adaptive response across climatically-contrasting Italian environments and implications for selection

White lupin (Lupinus albus) and narrow-leafed lupin (L. angustifolius) have special interest as high-protein feed crops but their cultivation is limited by low grain yields. This study aimed to support breeding programs targeting Italy or other climatically variable south-European regions by investigating within-species adaptation patterns across contrasting Italian environments. An additional aim was comparing species for yielding ability. Eight narrow-leafed and six white lupin cultivars featuring different origin, phenological type (Mediterranean in both species; winter in white lupin; spring in narrow-leafed lupin) and plant architecture (determinate or indeterminate in both species; tall or dwarf in white lupin) were evaluated in a Mediterranean and a subcontinental-climate site under autumn and late-winter sowing. Additive main effects and multiplicative interaction was preferable to joint regression for modeling yield responses. In both species, cross-over GE interaction was observed (P < 0.05), autumn-sown Mediterranean and subcontinental environments were the most-contrasting for GE effects, and widely adapted material included cultivars of Mediterranean phenological type with indeterminate growth. Material with determinate growth was not among the best-yielding entries in any environment, whereas a dwarf winter-type white lupin entry was specifically adapted to autumn-sown subcontinental environments. White lupin displayed larger genetic variation than narrow-leafed lupin for phenology and other traits. Relationships of morphophysiological traits with grain yield were environment-specific and were locally high for some white lupin traits (early flowering, long reproductive phase, high aerial biomass, low proportion of pod wall). White lupin exhibited higher yielding ability than narrow-leafed lupin in all environments but the late-winter sown Mediterranean one, when comparing locally top-yielding cultivars.     

Biplot analysis of trait relations of white lupin in Spain

A 2-year study of autumn-sown white lupin (Lupinus albus L.) was conducted under rainfed Mediterranean conditions in southern Spain. 108 landraces were evaluated for yield and major phonological and plant structural characteristics. Path coefficient and Genotype-Trait (GT) biplot analysis were used. Applying both types of analyses to the multiple trait data revealed that GT biplot graphically displayed the interrelationships among traits and facilitated visual comparison of accessions and selection. Wide variation was observed for trait phenology (dates of flowering and maturity), plant structure (plant and first order inflorescence height) and yield characters (first order branches, first order inflorescence and total yield). It was found that the accessions with the highest yields were the tallest and the latest to flower, both on the mainstem and on the lowest first order branch, and also were the latest to mature. GT biplots also had suggested as the accessions have been displayed according to their origins. The results showed that foreign germplasm may be an important material for improving some yield components such as number of pods and seeds per plant of locally adapted lupins in Spain. This revised version was published online in July 2006 with corrections to the Cover Date.     

Breeding for resistance to fusarium oxysporumF. SP. tulipae in tulip (tulipaL.).2. phenotypic and genotypic evaluation of cultivars

Summary Fusarium bulb rot is a serious tulip disease. Breeding for resistance may contribute considerably to a solution of the problem.It has been demonstrated that juvenile and adult bulbs of the same cultivars in Fusarium contaminated soil showed good agreement in degree of resistance.From an incomplete diallel cross of these cultivars second-year bulblets of 62 progenies were planted in both contaminated and non-contaminated soil. The percentages of non-diseased bulbs harvested provided a criterion for resistance. The analysis of combining ability for the degree of resistance revealed that both the mean square of GCA and that of SCA were significant. The relative magnitudes of the GCA and SCA mean squares suggest that resistance is governed primarily by additive gene action. The GCA of individual parents could be estimated and tested. In general it corresponded with their phenotypic behaviour.     

Inheritance of resistance to black rot (Xanthomonas campestris pv. Campestris) in cauliflower (Brassica oleracea var. Botrytis)

Summary Black rot disease caused by Xanthomonas campestris pv. campestris is a limiting factor in the commercial production of the cauliflower crop. Crosses were attempted between SN 445, a mid season cultivar resistant to black rot and two highly susceptible commercial cultivars (Pusa Snowball-1 and K-1). Studies of the F₁'s, F₂'s and back crosses indicated that SN 445, carries a dominant gene imparting resistance to black rot.     

Crown depth and susceptibility to crown rot in wheat

Sources of partial resistance to crown rot caused by Fusarium pseudograminearum are detected in mature plants grown in artificially inoculated soil in the field. The resistance in most but not all of these sources can also be detected in seedlings. In order to determine whether partial resistance is related to depth of crown formation, this character was measured in 13 cultivars/lines with a range of reaction to crown rot. It was also measured in doubled haploid plants from the cross, Batavia/2–49. Crown depths varied from 17.1 mm to -2.3 mm (above ground) in pots in a waterbath at 25 ^°C and from 43.5 mm to 20.7 mm when plants were grown in the field. The correlation coefficient between relative susceptibility to crown rot (Field test) and crown depth of 13 cultivars/lines was 0.57 (p ≤ 0.05). With the exception of the cultivars, Sunco and Pelsart, partial resistance to crown rot was inversely related to depth of crown formation. This indicates that depth of crown formation may be partly responsible for the reaction of a cultivar/line to crown rot. Depth of crown formation was also measured in susceptible and partially resistant cultivars/lines grown from seed planted at different depths. As depth of seeding increased, depth of crown formation in partially resistant and susceptible cultivars/lines increased in similar proportions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Identification of levels of resistance to cassava root rot disease (<Emphasis Type="Italic">Botryodiplodia theobromae</Emphasis>) in African landraces and improved germplasm using <Emphasis Type="Italic">in vitro</Emphasis> inoculation method

Cassava root rot disease is an increasing problem in Africa where yield losses of about 80% have been recorded. We evaluated 290 African landraces and 306 improved genotypes from the germplasm collections of the International Institute of Tropical Agriculture (IITA), for sources of resistance using root slice laboratory assay. Disease severity was assessed quantitatively by direct percentage estimation (PS) and by use of a rating scale (RS). Both methods of assessment were compared for identification of variability in the germplasm, and genotypes were classified into response groups using an enlarged rank-sum method that combined the PS and RS assessments. The two scoring methods revealed continuous variation (P < 0.001) for resistance in the sets of germplasm. Disease assessments based on PS and RS were highly correlated in both the improved germplasm (r = 0.75) and the landraces (r = 0.72). Based on PS assessment, 50 improved genotypes (16.3%) and 53 landraces (18.3%) showed significantly lower disease scores than the resistant control. The rank-sum method separated each set of collections into highly resistant, resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible groups. Fifty-nine improved genotypes (16.4%) and 61 African landraces (16.9%) were identified as either highly resistant or resistant. Generally, these genotypes exhibited resistance by limiting the growth of the pathogen (reduced amount of invaded surface area). This type of rate-reducing resistance is highly heritable and a quantitative trait which can be harnessed in breeding. Genotypes subsets were identified for further studies into the genetic basis of resistance to root rot disease.     

Constitutive expression of Cry proteins in roots and border cells of transgenic cotton

Transgenic cotton plants expressing Cry1Ac and Cry2Ab, from the soil bacterium Bacillus thuringiensis (Bt), provide effective control of certain lepidopteran pests, however, little is known about the proteins below ground expression. We used ELISA to quantify in vitro expression of the Cry1Ac and Cry2Ab proteins in mucilage, root border cells and root tips in five transgenic cultivars of cotton compared to conventional cultivar Sicot 189. Expression of Cry proteins in roots and border cells of the transgenic cotton cultivars was constitutive and at detectable levels, with Cry1Ac and Cry2Ab protein expression ranging from <20 ppb to >100 pbb. To determine if genetically modified cotton demonstrated simple differences in properties of the root, when compared to an elite parental line (cv. Sicot 189), we enumerated border cells on seedling radicles. Border cell counts of 14 cultivars ranged from 0.2 to 1.1 × 10⁴ cells per root tip with an average of 5 × 10³ border cells. Border cell production in the transgenic cultivars was generally similar to that of both donor and elite parents, the exception being the cultivar Sicot 189, which had substantially more border cells than all of its transgenic derivatives. Comparison of border cell number with varietal disease resistance ranking found a limited relationship (r ² = 0.65, n = 7) between border cell numbers and the commercial resistance rank against Fusarium wilt of cotton. The implications of differences in cotton cultivar border cell number and root tip expression of Cry proteins for plant–microbe interactions in the rhizosphere and the soil ecosystem are yet to be resolved.     

Screening of Portuguese cole landraces (Brassica oleracea L.) with Leptosphaeria maculans and Xanthomonas campestris pv. campestris

Summary Fifty-six landraces of Portuguese coles (Brassica oleracea l.), representing fourteen morphotypes, were screened for resistance to Leptosphaeria maculans at the cotyledon stage. Three isolates of the pathogen belonging to three pathogenicity groups were used in the screening. The mean disease interaction phenotype of the B. oleracea landraces with the L. maculans isolates confirmed their differences in pathogenicity. When compared to pathogenicity grouping using a B. napus differential set, a different classification was observed on B. oleracea for the three L. maculans isolates, suggesting possible differences in the genetic interaction between the two plant species and the pathogen. Most of the Portuguese cole landraces were found to be susceptible to all three isolates of L. maculans, although a few have shown intermediate interaction phenotype. Some accessions, on the other hand, elicit a differential reaction with the three isolates tested, and can be further selected to be used in host differential sets or in breeding for resistance to black leg.Fifty-four landraces of Portuguese coles, representing eleven morphotypes, were also screened in the field for resistance to Xanthomonas campestris pv. campestris. A good level of resistance to the bacterium was found in several of the morphotypes.Accessions of the Penca type, particularly, were identified as highly resistant. Landraces belonging to the same Portuguese cole group presented a similar range of mean interaction phenotype with the bacterium. Some Portuguese landraces of B. oleracea are potential sources for use in breeding programs for black rot resistance.     

Screening of Portuguese cole landraces (Brassica oleracea L.) with Peronospora parasitica and Plasmodiophora brassicae

Summary Forty-four landraces of Portuguese coles (Brassica oleracea L.), representing different morphotypes, were screened at the cotyledon stage for downy mildew resistance, caused by Peronospora parasitica. Two isolates of the pathogen, PHW 630 and PHW 828, were used in the experiment. The mean disease interaction phenotype varied among the landraces. Overall, the Portuguese coles have shown resistance to both isolates, particularly to isolate PHW 828. Some landraces were identified with differential reaction to the two P. parasitica isolates. Some of the Portuguese coles are, therefore, good sources of resistance genes to P. parasitica, and could be used in breeding programs or in the development of a downy mildew host differential set. Among the morphotypes tested, Couve Algarvia (ISA 207), Couve Galega (ISA 243 and 187) and Couve Glória de Portugal (ISA 84) have presented the highest resistance interaction. For the development of host differential sets, the landraces ISA 2 (Penca de Mirandela), ISA 35 (Couve de Valhascos) and ISA 600 (Penca Espanhola) could be further selected for the differentiation of P. parasitica isolates. They are resistant to PHW 828 and susceptible to PHW 643.The same morphotypes and landraces were also screened at the seedling stage for resistance to clubroot, caused by Plasmodiophora brassicae Woron.. Although some variation for resistance could be noticed in some the landraces tested, mainly Galega kale types, none of them presented a sufficient level of resistance as to be directly be useful in breeding for resistance to race 6 of P. brassicae.     

Measuring field resistance of cabbage cultivars to black rot

Summary Disease progress and gradient curves of black rot on cabbage were evaluated in field plots of the cultivars Bartolo, Erdeno, Perfect Ball, and Roxy in The Netherlands during 1991 and 1992. Plots were inoculated by single sources in the centre of each plot. Individual plants were examined for disease incidence and severity. Disease progress was described by the Gompertz model. The overall measure of absolute rate (disease progress rate r multiplied with maximum disease intensity K) was used to compare cultivar effects on disease progress. Disease gradients were described by the negative exponential model. The percentile distance (distance from the source at which disease intensity reached 1% of the empirical maximum disease intensity) was used to compare cultivar effects on disease spread. Disease severity is more sensitive than disease incidence to calculate the disease progress and spread of black rot. Measures of progress and gradient were about equally effective to screen cultivars for field resistance to black rot. Perfect Ball was the most susceptible, Erdeno and Bartolo were intermediate and Roxy was the most resistant for incidence and severity measures. Increased levels of field resistance reduced the development of black rot in time and in space. Field resistance of black rot is thought to be composed of several mechanisms. Microplots provide a good instrument for the assessment of small differences in field resistance, expressed equally well in disease progress as in disease gradient curves.     

Increasing resistance to Fusarium crown and root rot in asparagus by gametophyte selection

In garden asparagus, Fusarium crown and root rot is the main cause of crop decline. Since chemical treatments are inefficient, efforts should focus on the development of resistant cultivars to control the disease. Toxic culture filtrate (TCF) of F. oxysporum has affected asparagus pollen germination and tube growth. Consequently, gametophyte selection was evaluated to ascertain if the application of selective agents at this level could increase selection efficiency. Two susceptible pistillate plants and one tolerant and one susceptible staminate plants were used in controlled crosses. Before pollination, a drop of a germination vehicle with TCF or without it was applied to the stigmas. Some pollinated pistils were fixed and analyzed by fluorescence microscopy; the rest were left on the plant for seed production. Fifty to 200 seeds were obtained per treatment combination (staminate plant x pistillate plant x pollination vehicle). The derived plantlets were inoculated in vitroand evaluated for disease symptoms. The application of TCF to stigmas reduced pollen germination and tube growth compared with untreated controls,regardless of the genotypic combination. Pollen germination and tube growth was poorer for the tolerant staminate genotype than for the susceptible one. When the TCF was applied, the number of seeds per pollination in comparison with the controls diminished only when the susceptible genotype was the pollinator. The percentage of affected root area of the progenies obtained after applying the TCF was lower than in the controls only when the tolerant genotype was the pollinator. Increasing Fusarium resistance in asparagus by means of gametophyte selection seems feasible. This revised version was published online in August 2006 with corrections to the Cover Date.     

In vitro techniques for selecting wheat (Triticum aestivum L.) for Fusarium-resistance. II. Culture filtrate technique and inheritance of Fusarium-resistance in the somaclones

Summary Calli of resistant, intermediary and susceptible wheat (Triticum aestivum L.) varieties were selected using culture filtrates of Fusarium graminearum and F. culmorum and the regenerants were evaluated for resistance up to R₃. Czapek-Dox broth medium was inoculated with mycelia of Fusarium isolates and incubated for 2–6 weeks. Filtrates were added to MS callus growing medium, then 5 weeks-old calli were transferred onto this medium (MST) for 4–5 weeks. MST containing 30% filtrate was found to be suitable for selection. Resistant calli were transferred again to fresh MST for further two selection cycles. The surviving calli produced less fertile regenerated lines (R₀) than the non-selected ones. Among 18 R₁ lines tested for Fusarium-resistance in the seedling stage by artificial inoculation in the greenhouse, two (11.1%) were significantly more resistant, one (5.6%) was more susceptible than the original cultivar and the rest (83.3%) behaved similarly to the donor plants. Among unselected R₃ lines of three varieties, practically the same number of resistant plants were found as among the related selected ones. When the R₃ selfed generations obtained through double-layer and culture filtrate selection techniques were tested for Fusarium-resistance, 35.7% of the lines were found to be more resistant than the original cultivars, none was more susceptible and 64.3% had a reaction similar to that of the source materials. Thus, inheritance of the disease reaction was not stable in all cases. Success of in vitro selection for Fusarium-resistance depended also on the genotype, and toxin analysis showed that although being effective, the selective media contained deoxynivalenol only exceptionally. In selecting wheat for Fusarium-resistance in vitro, the culture filtrate technique proved better than the double-layer procedure.     

The challenges of maintaining wheat productivity: pests, diseases, and potential epidemics

Knowing pests and diseases that may cause injuries and are likely to affect plant health and quality is critical to minimizing the gap between attainable yield and actual yield. In this paper, we highlight concepts and strategies aimed at controlling major biotic constraints affecting wheat in intensive production systems and present emerging challenges, with a special attention to the developing world. Disease epidemics result from the combination of inoculum, favorable environment, and host susceptibility. Changes in cropping systems as a result of adoption of conservation agriculture may have serious implications. Necrotrophic pathogens such as those responsible for tan spot or septorias are likely to emerge, and Fusarium head blight may increase. However, resistance breeding combined with rotations, timely sowing, and irrigation or even fungicide utilization, if affordable, are part of integrated crop management practices that can minimize losses. In South Asia, the effect of spot blotch, a devastating foliar disease caused by Cochliobolus sativus, can be minimized by reducing physiological stress through timely sowing and adequate use of fertilizers, which demonstrates the complex relationships among crop physiology, disease resistance, and yield. Although some root rots that induce premature death of tillers in cooler high-yielding humid environments can be important, the dryland crown rot (Fusarium spp.), common root rot (C. sativus), and the cereal nematode (Heterodera spp. and Pratylenchus spp.) should not be ignored. These are all known to be much more damaging under suboptimal moisture (rainfed or supplementary irrigation), particularly where plant growth is stressed. Climate change is likely to modify the wheat disease spectrum in some regions, and pathogens or pests considered unimportant today may turn out to be potential new threats in future.     

Selection for resistance to Plasmodiophora brassicae Wor. in oriental subspecies of Brassica rapa L.

Summary Selection for resistance to Plasmodiophora brassicae Wor. in oriental groups of Brassica rapa L.Two hundred and sixty-five cultivars of leafy, oriental bassicas were tested for resistance to 18 collections of Plasmodiophora brassicae, the causal agent of clubroot. The tests were conducted in the greenhouse at low and high level inoculum concentrations. Eleven cultivars of B. rapa pe-tsai, five cultivars of B. rapa pak-choy and three cultivars of B. rapa choy-sum consistently segregated for resistance at the lower concentration of inoculum (1000 spores/ml). All 265 cultivars were susceptible at the higher concentration (1 000 000 spores/ml). Three cultivars were used in pedigree and recurrent selection schemes for increased resistance. After three cycles of selfing resistant individuals, significantly more resistant S₃ lines were derived from each cultivar. Lines derived from two cultivars. Chinese White and PI 257236, continued to improve with each cycle of selection and demonstrated increased resistance to higher levels of inoculum (up to 1 000 000 spores/ml) New cultivars based on intercrosses of S₂ resistant individuals also had significantly better resistance than the original cultivar. After two cycles of selection in the third cultivar, PI 419007, resistance did not increase and its S₂ mass did not differ significantly from the original cultivar. Evidence that indicates resistance is pathotype-non-differential and offers an alternative to major gene, pathotype-differential types of resistance currently being introduced to the leafy oriental brassicas from other Brassica rapa groups.     

Heritability of resistance to brown spot and root rot of narrow-leafed lupins caused by Pleiochaeta setosa (Kirchn.) Hughes in field experiments

Resistance to brown spot (BS) and Pleiochaeta root rot (PRR) in narrow-leafed lupin (Lupinus angustifolius L.) was assessed on a broad range of breeding lines and cultivars in field trials in Western Australia in 1985 and 1986. Both diseases are caused by Pleiochaeta setosa (Kirchn.) Hughes. Lines were grown in 5m × 1m plots in randomized complete block experiments with various disease pressures associated with cropping history — first, second and third successive lupin crops after cereals at one site in 1985, and first and second lupin crops at two sites in 1986. Best linear unbiased predictors (BLUPs) of defoliation caused by BS across experiments ranged from 64% to 123% of ‘Gungurru’, and BLUPs for PRR lesion severity ranged from 82% to 118% of ‘Gungurru’. For both diseases, genotypic variance was several times greater than genotype × environment variance, but error variance was relatively low for BS and high for PRR. Consequently, broad sense heritability (h²) for BS resistance was high in the seven experiments (range 0.89–0.94) but low for PRR resistance (range 0.00–0.53). There was a moderate correlation between BLUPs for resistance to BS and PRR across experiments (r = 0.36, P < 0.05). Genotypic correlations between resistance to BS and PRR were estimated at 0.57 ± 0.20 and 0.75 ± 0.31 in two experiments in 1985. Breeding progress is likely to be high for BS resistance and there may be slight improvements in PRR resistance associated with BS resistance. However, this field technique is not suitable for rapid breeding progress for PRR resistance.     

Evaluation of landrace topcross hybrids of pearl millet for arid zone environments

Pearl millet (Pennisetum glaucum (L.) R. Br.) cultivars for marginal, arid environments need to combine the adaptation to stress conditions of indigenous landraces with an improved yield potential and disease resistance, to allow them to both perform well in farmers fields and to meet the requirements for cultivar release. This paper evaluates landrace-based topcross hybrids (adapted landraces crossed on high-yielding male-sterile lines), as a quick and efficient way of achieving this objective. Topcross hybrids showed a consistent increase in biomass production across all test environments, including the harsh arid zone environments. Depending upon the plant type of the male-sterile used to make the hybrid, this was expressed as increased grain yield only, or increased grain and fodder yields. The downy mildew (Sclerospora graminicola) reaction of the topcross hybrids was determined by the reaction of the male-sterile line used, with the resistant male-sterile producing resistant topcross hybrids and vice-versa. Topcrossing adapted landraces on high-yielding male-sterile lines thus provides an opportunity to improve disease resistance and grain and/or fodder yields, with no apparent loss of adaptation to the marginal environments in which the landraces have evolved.ICRISAT Journal Article no. 1575     

Genetic control of Russian wheat aphid (Diuraphis noxia) resistance in wheat accession PI 47545

The Russian wheat aphid, Diuraphis noxia (Mordvilko), is a major pest of cereal crops in many areas of the world, causing serious reduction in grain yield in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). Incorporating genetic resistance to D. noxia into wheat cultivars is paramount to effectively reduce damage inflicted by this pest. Genetic resistance to D. noxia has been identified in wheat, barley and rye germplasm, and several resistance genes are available for use for cultivar improvement. In the United States of America, only a few Russian wheat aphid (RWA) resistant winter wheat cultivars are currently available, and these cultivars contain only one of the six known RWA resistance genes. The objective of this study was to determine the inheritance of RWA resistance in wheat accession PI 47545, using a screening method based on differences in the leaf morphology of resistant and susceptible types following insect challenge. PI 47545 was selected for study, since it displayed high levels of resistance in a white-grained wheat background, the predominant wheat class produced in the Pacific Northwest of the USA. Segregation analysis was conducted on an F₂ population developed by cross-hybridizing the susceptible soft white winter wheat cultivar ‘Daws’ to the resistant accession PI 47545. Russian wheat aphid screening data from this population indicated that the resistance in PI 47545 is controlled by a single, dominant gene (χ² = 1.72; p ≤ 0.189). This revised version was published online in August 2006 with corrections to the Cover Date.     

Breeding for resistance to Phialophora cinerescens (Wr.) van Beyma in glasshouse carnations (Dianthus caryophyllus L.)

Summary A breeding programme is described, aimed at introducing resistance to Phialophora cinerescens in glasshouse carnations of both the standard and the spray type. Four resistant clones, selected from seed-grown garden cultivars, served as resistant parents; the susceptible parents included the major glasshouse cultivar William Sim and some of its mutants and a few other American, French and Italian cultivars.In three generations of breeding, with extensive screening of young seedling populations, an adequate level of resistance had been reached. Selection procedure was henceforth changed to allow for primary selection on quality and productivity, followed by clonal resistance tests.Inheritance of resistance appears to be mainly additive; at least two gene pairs are likely to be involved. Under prolonged high infection pressure a significant non-additive variance can be demonstrated.     

Comparative genetic analysis of field resistance to downy mildew in the lettuce cultivars ‘Grand Rapids’ and ‘Iceberg’

Downy mildew on lettuce is currently controlled using host resistance genes (Dm genes) that confer race-specific resistance in seedlings. Field resistance (FR) that is active in adult plants but not seedlings was identified in the cvs. Grand Rapids and Iceberg. The goal of our study was to evaluate the utility of Grand Rapids as a source of novel Bremia resistance alleles, particularly in comparison with Iceberg. To measure FR, downy mildew symptoms were evaluated following natural infection in field experiments. The responses of Grand Rapids and Iceberg were similar in many respects. Although both cultivars had a small percentage of plants exhibiting disease symptoms, the average disease ratings were as low as for cultivars with effective Dm genes. We observed no evidence for race specificity. FR was effective over 3 years of our study, despite documented variation within pathogen populations. Both cultivars lacked all known seedling resistance genes except Dm13, which was not responsible for the resistance observed in field experiments. Similar segregation of FR was observed in F₂ populations for both Grand Rapids and Iceberg. The presence of highly susceptible families within Grand Rapids × Iceberg populations suggested the presence of at least one unique resistance allele in each cultivar. Preliminary genetic analysis of FR from Grand Rapids revealed a high estimate of narrow-sense heritability that suggested simple inheritance, but single gene models did not fit the observed data. Our results suggest that Grand Rapids may represent an underutilized resource for controlling downy mildew in lettuce.     

Application of multi-phase experiments in plant pathology to identify genetic resistance to <Emphasis Type="Italic">Diaporthe toxica</Emphasis> in <Emphasis Type="Italic">Lupinus albus</Emphasis>

Phenotyping assays in plant pathology using detached plant parts are multi-phase experimental processes. Such assays involve growing plants in field or controlled-environment trials (Phase 1) and then subjecting a sample removed from each plant to disease assessment, usually under laboratory conditions (Phase 2). Each phase may be subject to non-genetic sources of variation. To be able to separate these sources of variation in both phases from genetic sources of variation requires a multi-phase experiment with an appropriate experimental design and statistical analysis. To achieve this, a separate randomization is required for each phase, with additional replication in Phase 2. In this article, Phomopsis leaf and pod blight (caused by Diaporthe toxica) of Lupinus albus was used as a case study to apply a multi-phase experimental approach to identify genetic resistance to this pathogen, and demonstrate the principles of sound experimental design and analysis in detached plant part assays. In seven experiments, 250 breeding lines, cultivars, landraces, and recombinant in-bred lines from a mapping population of L. albus were screened using detached, inoculated leaves, and/or pods. The experimental, non-genetic variance in Phase 2 varied in magnitude compared to the Phase 1 experimental, non-genetic variance. The reliability of prediction for resistance to Phomopsis pod blight was high (mean of 0.70 in seven experiments), while reliability of prediction for leaf assays was lower (mean 0.35–0.51 depending on the scoring method used).