Species specific primers for identification of Alternaria solani,in combination with analysis of the F129L substitution associates with loss of sensitivity toward strobilurins

A species specific forward primer was designed in order to identify the phytopathogenic fungus Alternaria solani, which causes early blight on potato. The reverse primer came from another survey of the American population of A. solani. The combination of these two primers can be used both as molecular identification of A. solani as well as sending the PCR product for sequencing in search for the F129L substitution associated with loss of sensitivity toward fungicides based on strobilurins. The diagnostic method has been successfully used when identifying the causal agent of lesions on potato leaflets during large field assays.     

Assessing fungicide resistance in populations of Alternaria in Idaho potato fields

Early blight, caused by the fungus Alternaria solani and brown leaf spot, caused by Alternaria alternata, are important diseases of potato crops in Idaho. In recent years growers have reported a reduction in efficacy of fungicides traditionally used in the past decade to control early blight. In 2009, a collection of A. solani 39 isolates were screened for resistance to azoxystrobin, pyraclostrobin, boscalid and famoxadone. Fungicide sensitivity testing was done using spiral plate dilution gradients. Results showed that of 39 isolates screened, all were resistant to azoxystrobin and three were resistant to boscalid. None were resistant to pyraclostrobin or famoxadone. In summer 2010, more isolates were collected (9 A. alternata and 26 A. solani) and the survey was expanded to include more fungicides with four different modes of action that targeted succinate dehydrogenase (SDH), methionine biosynthesis, mitochondrial respiration and multi-site contact activity. New isolates of A. solani and A. alternata were also collected from two additional sites. The results showed that 57% of the isolates were resistant to boscalid as well as an average of 63% of the isolates being resistant to the strobilurin fungicides. Seven and 15% of isolates were resistant to penthiopyrad (an SDH inhibitor), and pyrimethanil (a methionine biosynthesis inhibitor), respectively. However, none of the isolates were resistant to fluopyram (an SDH inhibitor) or a mixture of fluopyram and pyrimethanil. Although there appears to be cross resistance developing in Alternaria spp. to some of the new SDH inhibitors like penthiopyrad, others such as fluopyram are still showing limited to no resistance development in Alternaria spp. in Idaho.     

Sensitivity and cross-resistance patterns to demethylation-inhibiting fungicides in California populations of Alternaria alternata pathogenic on pistachio

Alternaria late blight (ALB) caused by Alternaria spp. is an annual production concern for pistachio growers in California. In this study, isolates of Alternaria alternata collected from California pistachio orchards between 1998 and 2003 (population A, n = 46) and in 2010 (population B, n = 38) prior to the registration and use of sterol demethylation-inhibiting (DMI) fungicides for ALB control, were tested for their sensitivity to difenoconazole, propiconazole, and tebuconazole using an in vitro mycelial growth assay. The 50% effective dose (EC₅₀) values for isolates in population A to difenoconazole, propiconazole, and tebuconazole, respectively, ranged from 0.02 to 0.82 μg/mL (mean = 0.17), 0.25–5.73 μg/mL (mean = 1.29), and 0.02–2.76 μg/mL (mean = 0.96), and from 0.02 to 0.93 μg/mL (mean = 0.21), 0.13–5.36 μg/mL (mean = 1.25), and 0.17–5.47 μg/mL (mean = 1.03) for those in population B. Among 65 isolates collected in 2012 from orchards with very limited exposure to difenoconazole, propiconazole or metconazole (population C, n = 65), the EC₅₀ values for tebuconazole ranged from 0.02 to 2.99 μg/mL (mean = 0.51), while EC₅₀ values for difenoconazole of 55 of these isolates varied from 0.01 to 0.44 μg/mL (mean = 0.06). The DMI-exposed population C was found to be on average two to four times less sensitive compared with the populations A and B. Pearson correlation analyses of EC₅₀ values for the three fungicides showed significant positive correlations between the sensitivities of tebuconazole and propiconazole (P < 0.01, r = 0.32), tebuconazole and difenoconazole (P < 0.01, r = 0.26), and difenoconazole and propiconazole (P < 0.01, r = 0.40). Results indicate a clear difference in fungicide intrinsic activity, with difenoconazole being more active than the two other DMIs. Although wide variations in sensitivities for tebuconazole and propiconazole were observed in the non- and DMI-exposed Alternaria populations, efficacy of DMI products has been excellent against ALB. The data collected here will be crucial for the rational use of DMIs in fungicide spray programs for ALB management and serve as a reference to detect any shifts in A. alternata sensitivity to these fungicides in subsequent years as they become more frequently used in California pistachios.     

Growth promotion and induction of resistance in tomato plant against Xanthomonas euvesicatoria and Alternaria solani by Trichoderma spp.

In tomato crop, the induction of resistance emerges as an important alternative for achieving the reduction of chemicals in disease control. This study aimed to evaluate the ability of 28 Trichoderma isolates to promote the growth of tomato seedlings and to induce systemic resistance (ISR) against Xanthomonas euvesicatoria and Alternaria solani, the causal agents of bacterial spot and early blight, respectively. Twelve isolates promoted the increase of plant dry matter mass (DMM) above 100%, showing the great potential of these strains. All isolates were able to colonize the root system of tomato plants. The plant growth-promoting isolates were further evaluated for potential elicitation of ISR. Treatment of the soil with all Trichoderma isolates provided protection in tomato plants from 24.13 to 95.94% against X. euvesicatoria and 30.69 to 95.23% against A. solani. The most efficient isolates in reducing the severity of bacterial spot and early blight were the isolates IB 28/07, IB 30/07, IB 37/01 and IB 28/07, IB 30/07 and IB 42/03, respectively. The effect of different time intervals between Trichoderma application and inoculation with pathogens in inducing systemic resistance in tomato plants was evaluated for the isolate IB 28/07. IB 28/07 conferred protection against both diseases at all time intervals, confirming the ability of the isolate to reduce the severity of these diseases up to 21 days after treatment of tomato plants. In vitro assays revealed that all isolates of Trichoderma were able to degrade cellulose. Only the isolate IB 34/08 showed antagonistic activity against X. euvesicatoria and none caused reduction in the in vitro mycelial growth of A. solani. Trichoderma isolates were identified at species level by DNA sequencing.     

Suppression of rice sheath blight disease using a heat stable culture filtrate from Streptomyces philanthi RM-1-138

Streptomyces philanthi RM-1-138, isolated from the rhizosphere soil of chili pepper in southern Thailand, was investigated for its antagonistic activity against phytopathogenic fungi. In dual culture on glucose yeast-malt extract (GYM) agar plates, this strain suppressed the mycelial growth of all seven plant pathogenic fungi tested (Rhizoctonia solani PTRRC-9, Pyricularia grisea PTRRC-18, Colletotrichum gloeosporioides NBCRSR-3, Colletotrichum capcisi NBCRSR-15, Ganoderma boninense NBCRSR-26, Fusarium fujikuroi PTRRC-16 and Bipolaris oryzae PTRRC-36) with an 82.2–89.2% inhibition and that was most pronounced on R. solani PTRRC-9. Heat treatment of the culture filtrate from growing R. solani PTRRC-9 at 40 °C, 60 °C, 80 °C, and 100 °C for 30 min and 121 °C for 15 min had no negative effect on the inhibitory activity against R. solani PTRRC-9 tested on both solid and liquid culture. The effective dose (>80% inhibition) of culture filtrate in liquid culture was at 5.0% (v/v) while it was at 10% (v/v) on the solid medium. This effectiveness was similar to those of the four chemical fungicides tested. The effect of S. philanthi RM-1-138 against R. solani PTRRC-9 was investigated using SEM and TEM. The compounds produced by S. philanthi RM-1-138 induced alterations to the cell-wall structure of R. solani PTRRC-9, that resulted in the loss of cytoplasm materials by partial lysis. The greenhouse experiment revealed that using either the culture filtrate or the autoclaved culture filtrate from S. philanthi RM-1-138 effectively suppressed rice sheath blight disease by up to 65.6 and 60.8%, respectively.     

Sources and seasonal dynamics of Alternaria inoculum associated with leaf blotch and fruit spot of apples

Alternaria leaf blotch and fruit spot caused by Alternaria spp. cause annual losses to the Australian apple industry. Control options are limited, mainly due to a lack of understanding of the disease cycle. Therefore, this study aimed to determine potential sources of Alternaria spp. inoculum in the orchard and examine their relative contribution throughout the production season. Leaf residue from the orchard floor, canopy leaves, twigs and buds were collected monthly from three apple orchards for two years and examined for the number of spores on their surface. In addition, the effects of climatic factors on spore production dynamics in each plant part were examined. Although all four plant parts tested contributed to the Alternaria inoculum in the orchard, significant higher numbers of spores were obtained from leaf residue than the other plant parts supporting the hypothesis that overwintering of Alternaria spp. occurred mainly in leaf residue and minimally on twigs and buds. The most significant period of spore production on leaf residue occurred from dormancy until bloom and on canopy leaves and twigs during the fruit growth stage. Temperature was the single most significant factor influencing the amount of Alternaria inoculum and rainfall and relative humidity showed strong associations with temperature influencing the spore production dynamics in Australian orchards. The practical implications of this study include the eradication of leaf residue from the orchard floor and sanitation of the canopy after harvest to remove residual spores from the trees.     

Spray deposition assessment and benchmarks for control of Alternaria brown spot on mandarin leaves with copper oxychloride

Inadequate disease control on citrus foliage and fruit is often attributed to insufficient fungicide spray deposition on target surfaces. This study describes a novel spray deposition assessment protocol and determines deposition benchmarks indicative of the biological effectiveness for better interpretation of spray deposition results. Suitability of a yellow fluorescent pigment as tracer for copper oxychloride deposition was demonstrated through its similar particle concentration and size. Spray deposition assessment of spray targets, which were sprayed with a mixture that included the fluorescent pigment, involved photomacrography of whole leaf or fruit surfaces, followed by digital image analyses. This protocol proved to be very accurate in determining the quantity and quality of deposition. To determine deposition benchmarks, detached young ‘Nova’ mandarin leaves were sprayed with copper oxychloride and fluorescent pigment at different concentrations (0.1–2 times the recommended concentration) and spray deposition assessed. Subsequently, leaves were spray inoculated with a spore suspension of Alternaria alternata [causal agent of Alternaria brown spot (ABS) of mandarins], moist-incubated for c. 48 h and symptom expression rated. A very good linear relationship was found between fungicide concentration, leaf area covered by fluorescent pigment particles (%FPC) (r = 0.879) and Cu residue analysis (r = 0.992). A von Bertalanffy growth curve best fitted the relation between ABS control and deposition quantity (%FPC) data (91% of the percentage variance accounted for) with a good correlation between observed and predicted values (r = 0.825). Benchmarks for 50% and 75% disease control were calculated as 2.07 %FPC and 4.14 %FPC, respectively. These corresponded with Cu residue levels of 59.4 and 91.0 mg kg⁻¹, respectively. These FPC benchmarks can be used to evaluate spray technology research, specifically for control of ABS and similar citrus fruit and foliar diseases.     

Temporal sensitivity ofAlternaria solani to foliar fungicides

Alternaria solani Sorauer (Ellis) is a causal agent of early blight of potato (Solanum tuberosum L.). Sensitivity to chlorothalonil, triphenyl tin hydroxide (TPTH), and mancozeb was determined for field isolatesof A. solani in 1998 and 1999. Specifically, the relative sensitivity ofA. solani to foliar fungicides in field populations collected from several commercial fields was evaluated over the course of two growing seasons. Sensitivity to these foliar fungicides was determined with anin vitro spore-germination assay method. The fungicide concentration that inhibited conidial germination by 50% (EC₅₀) was estimated for each isolate. Sensitivity ofA. solani isolates to TPTH and mancozeb varied little during the growing season, possibly because there were few TPTH and mancozeb applications made to the fields studied. At several locations, however, repeated exposure ofA. solani populations to chlorothalonil resulted in considerable variability in sensitivity, frequently causing isolates to have decreased sensitivity to this fungicide at the end of the growing season. In five of seven fields, isolates of A.solani collected at the end of the season were significantly less sensitive to chlorothalonil than isolates collected at the beginning of the season.     

Antifungal activity in vitro of Flourensia spp. extracts on Alternaria sp., Rhizoctonia solani,and Fusarium oxysporum

There are 32 species of Flourensia genus with 9 native to Mexico. These species contain compounds with potential use for pest control. In this paper, we report the antifungal activities of ethanol extracts from three endemic species in Coahuila state: Flourensia microphylla, Flourensia cernua, and Flourensia retinophylla. Also, preliminary information on the chemical composition of the extracts is included. Antifungal activity was tested against three pathogens attacking commercial crops: Alternaria sp., Rhizoctonia solani, and Fusarium oxysporum. The extracts concentration varied from 10 to 1500 μl l⁻¹. The ANOVA showed highly significant differences (P ≤ 0.01) with the extracts, the doses, and on the interaction extract × dose. Inhibition effect was observed from 10 μl l⁻¹ in all three species. Total inhibition was found only with F. cernua and F. retinophylla at 1000 μl l⁻¹ for R. solani, the three species inhibited the three pathogens at 1500 μl l⁻¹. Infrared analysis showed similar absorption signals for the extracts of the three species although in different concentration. This suggests that similar compounds may be present. The control of these pathogens by natural compounds is interesting both for environmental and economic reasons. The use of semiarid lands plants may improve the socioeconomic level of the people within the region.     

Effect of inoculum density and quantitative PCR-based detection of Rhizoctonia solani AG-2-1 and Fusarium avenaceum on canola

Canola seedling blight, caused by Rhizoctonia solani, and Fusarium spp., can result in large yield losses to canola (Brassica napus) at high inoculum pressure. The effect of inoculum density was studied by mixing different amounts of R. solani AG-2-1 and Fusarium avenaceum into a sterilized natural soil and soil-less mix (2:1, v:v) separately, and recording seedling emergence, damping-off and seedling height within ten days after seeding; root rot severity at 12 days after seeding and seed yield at harvest on canola cultivars ‘45H29’ and ‘73-77RR’. Root rot severity increased and emergence, plant height and seed yield decreased with increased inoculum density of both R. solani and F. avenaceum. For quantification of R. solani AG-2-1, a primer and TaqMan probe set (Rs21F/Rs21R/Rs21P) was designed based on the nuclear ribosomal internal transcribed spacer (ITS) region of R. solani AG-2-1. From a conventional PCR amplification, an 88-bp product was amplified from all isolates classified as AG-2-1 with the primers Rs21F and Rs21R. No product was amplified with DNA from isolates belonging to other anastomosis groups of R. solani, other pathogens or the host plant. By using quantitative PCR, DNA amounts as low as 100 fg of R. solani AG-2-1 were detected. The quantity of DNA from soil samples with different inoculum densities estimated using qPCR was highly correlated to the number of colony-forming units (cfu) obtained from the same soil samples for both R. solani AG-2-1 and F. avenaceum.     

Spring air temperature accounts for the bimodal temporal distribution of Septoria tritici epidemics in the winter wheat stands of Luxembourg

Septoria tritici is the causal agent of leaf blotch in wheat and among the most damaging fungal cereal pathogens in the humid regions of central Europe. The percentage of the leaf area colonized by S. tritici was recorded weekly between April and July every season between 2004 and 2010. A total of 11 cultivars with moderate susceptibility [ratings of 4–6 on a 1 (resistant) to 9 (susceptible) scale] were included. The disease level was assessed on the upper three leaf layers at 2 locations between 2004 and 2006 and at 3 locations between 2007 and 2010. The period between sowing and the point of time, when 50% of the leaf area was necrotized due to colonization by S. tritici (T₅₀) was estimated for each year, site, cultivar and leaf layer by non-linear regression. T₅₀ values followed a bimodal distribution with one maximum at 245 days after sowing (DAS; early epidemics) and one maximum at 270 DAS (late epidemics). Early epidemics were preceded by almost constant daily average temperatures of 13.2 ± 0.8 °C between 181 and 210 DAS. Late epidemics were preceded by an approximately linear increase in temperature from 8.7 ± 0.9 to 12.1 ± 0.9 °C during the same period of time. Based on these differences, it seems possible to predict whether an early or a late epidemic can be expected at least 35 days before the epidemic outbreak. Temperature sums calculated with a base temperature of 6.6 °C starting at sowing and ending when T₅₀ was reached were not significantly different between early and late epidemics (P = 0.73) and averaged 1721 ± 49°days. Fungicide applications, which resulted into a delay of the epidemic development similar to the difference between early and late epidemics, resulted in a yield increase between 11.7 and 12.6%.     

Plant population density,row spacing and hybrid effects on maize canopy architecture and light attenuation

Light attenuation within a row crop such as maize is influenced by canopy architecture, which has to be defined in terms of the size, shape and orientation of shoot components. Cultural practices that improve the efficiency of light interception affect canopy architecture by modifying such components. Our objectives were to: (i) determine the nature and timing of leaf growth responses to plant population and row spacing; (ii) analyze light attenuation within fully developed maize canopies. Field experiments were conducted at Pergamino (33°56′S, 60°34′W) and Salto (34°33′S, 60°33′W), Argentina, during 1996/1997 and 1997/1998 on silty clay loam soils (Typic Argiudoll) that were well watered and fertilized. Four maize hybrids of contrasting plant type were grown at three plant populations (3, 9 and 12 plants m⁻²) and two row spacings (0.35 and 0.70 m). Plant population promoted larger changes in shoot organs than did row spacing. As from early stages of crop growth, leaf growth (V₆–V₈) and azimuthal orientation (V₁₀–V₁₁) were markedly affected by treatments. Modifications in shoot size and leaf orientation suggest shade avoidance reactions, probably triggered by a reduction in the red:far-red ratio of light within the canopy. An interaction between hybrid and plant rectangularity on leaf azimuthal distribution was determined, with one hybrid displaying a random azimuthal leaf distribution under most conditions. This type of hybrid was defined as rigid. The other hybrids showed modified azimuthal distribution of leaves in response to plant rectangularity, even at very low plant populations. These hybrids were defined as plastic. Once maximum leaf area index (LAI) was attained light attenuation did not vary among hybrids and row spacing for plant populations ≥9 plants m⁻² (k coefficient: 0.55 and 0.65 for 9 and 12 plants m⁻², respectively). A more uniform plant distribution increased light attenuation (k coefficient: 0.37–0.49) only when crop canopies did not reach the critical LAI.     

Occurrence and characterization of fungi and oomycetes transmitted via potting mixtures and organic manures

A study was conducted to investigate the most common fungal and oomycete pathogens introduced into farms in Oman via potting mixtures and organic manures. A total of 37 commercial types of potting mixtures (2 local and 35 imported from overseas), 4 commercial types of organic manures and 11 non-commercial types of organic manures were included in the study. Identification of the isolated species was based on morphological characteristics, except for the most common species which were further identified using sequences of the internal transcribed spacer region of the ribosomal DNA (ITS rDNA). Fusarium spp. (14%), Pythium aphanidermatum (3%), Alternaria spp. (5%), Helminthosporium spp. (5%) and Cladosporium spp. (3%) were recovered at different frequencies from samples of potting mixtures. Fusarium solani (40%) and Fusarium equiseti (47%) were recovered at high frequencies from samples of organic manures. Isolations from organic manures also yielded Pythium periplocum (7%), Rhizoctonia solani (7%), Fusarium lichenicola (7%), Helminthosporium spp. (27%) and Alternaria spp. (27%). Trichoderma spp., Penicillium spp., Aspergillus spp. and Rhizopus spp. were found to be common in samples of potting mixtures and organic manures. Investigating sensitivity to hymexazol among 9 isolates of F. equiseti and 13 isolates of F. solani revealed variations among different isolates. The EC₅₀ values ranged from 1 to over 1200 (avg. 192 μg ml⁻¹) for F. equiseti isolates and from 135 to 789 (avg. 324 μg ml⁻¹) for F. solani isolates, indicating presence of resistance to this important fungicide among some Fusarium isolates. This appears to be the first report of contamination with R. solani, P. periplocum, F. solani, F. equiseti and F. lichenicola of organic manures. This study appears to report for the first time F. lichenicola in Oman and appears to be the first report of occurrence of resistance to hymexazol among F. equiseti and F. solani isolates.     

The heritability of resistance to early blight in diploid potatoes (Solanum tuberosum,subsp.Phureja andStenotomum)

The heritability of resistance to early blight caused byAlternaria solani (Ell. & Martin) Son was estimated for field grown, diploid potatoes at Fletcher, North Carolina in 1981. Fourteen breeding lines, selected from a random mated hybrid population ofSolanum tuberosum, subsp.phureja andstenotomum, were used. Resistance was measured as the slope obtained by regressing the logit of the disease proportion Y, measured as % defoliation, on time. A wide range of resistance was found. Narrow-sense heritability, as determined by offspring-midparent regression, on an individual plant basis, was calculated to be 0.825.     

A disease survey of Fusarium wilt and Alternaria blight on sweet potato in South Africa

A disease survey was conducted on sweet potato in the major production areas of South Africa in 2006-2008 to determine the importance of wilt disease (WD) and Alternaria blight (AB) caused by Alternaria bataticola. The disease prevalence, incidence and severity were assessed for both WD and AB in 58 sweet potato fields in seven provinces, and included both commercial and resource-poor growers. The prevalence of WD in commercial fields was significantly higher than in resource-poor fields; while disease incidence and severity were very low in both commercial and resource-poor fields. Soil pH showed a moderate negative linear correlation to WD severity. WD is at present considered a minor disease of sweet potato in South Africa, although local outbreaks can be damaging. AB had very low disease prevalence, incidence and severity levels in both commercial and resource-poor fields countrywide. However, one of the fields had moderately high disease incidence and severity levels, showing that the disease can be destructive if not controlled. AB should be considered a potentially destructive disease of sweet potato in South Africa. Fusarium oxysporum was consistently isolated from WD plants, with F. oxysporum f. sp. batatas identified, but other formae speciales were also associated with the disease.     

Elba: A late maturing,blight resistant potato variety

Elba is a high yielding cultivar which combines resistance to the golden nematode, foliar infection byPhytophthora infestans andAlternaria solani, andVerticillium wilt. Elba is a late maturing tablestock cultivar especially well adapted to organic soils. In small plots and on farmers’ fields it has demonstrated its worth in reducing the need for foliar fungicides to prevent blight.     

The effect of storage environment on the infection of potato tubers byAlternaria solani

Manipulation of storage environment to provide favorable conditions for wound healing immediately after harvest reducedAlternaria solani tuber infection. Prestorage of tubers at 15.6°C for three weeks before final storage at 10°C normally maintained for commercial storage of potato chip stocks resulted in fewer and smaller lesions than constant storage at 10°C or 4.4°C or prestorage for varying periods at these temperatures. Prestorage of potatoes at a low temperature (4.4°C) for 1–3 months resulted in moreA. solani infection suggesting that low temperatures may inhibit the wound healing process more than they reduce rates ofA. solani infection or disease development. Variations in relative humidities above 75% did not have an appreciable effect on the wound healing process nor onA. solani infection.     

The critical period for control of early blight (Alternaria solani) of potato

The purpose of this study was to identify when the critical period for control of early blight occurs and thus the need to initiate a spray schedule of protectant fungicides. The initiation of weekly fungicide spray schedules was staggered to identify the critical period. The accumulation of 400 P-Days, environmental conditions favorable for sporulation, spore dissemination and plant infection and airborne spores ofA. solani were detected prior to the critical period each year. Since early blight is a disease of old plants, host susceptibility appeared to be involved in the timing of the critical period in addition to favorable weather and the presence of the pathogen. A measure of potato plant development, and therefore susceptibility toA. solani, is needed to adequately predict the critical period. The accumulation of 400 P-Days may aid in the prediction of the critical period by estimating the time of plant susceptibility and therefore the timing of the first necessary fungicide spray.     

Inheritance of early blight resistance from open-pollinated 4×-2× potato hybrids

Early blight, caused byAlternaria solani Sorauer, is a serious disease of potatoes that occurs in most potatogrowing regions in the world. There is little resistance to early blight among commercial potato cultivars. However, resistance to early blight in diploid (Solanum phureja-S. stenotomum) potatoes has been identified, and was found to be highly heritable and readily transferred to the tetraploid level via4×-2× crosses. The purposes of this study were to identify good levels of early blight resistance in open-pollinated4×-2× (Solanum tuberosum×S. phureja-S. stenotomum) hybrids selected for horticultural characteristics, to estimate broad-sense heritability for early blight resistance in these hybrids, and to investigate the general and specific combining ability for resistance to early blight from some of these early blight resistant tetraploid selections. Four early blight resistant clones were crossed as female parents with four different male parents in a design II mating scheme to generate 16 families. Approximately 20 randomly chosen offspring per family were visually evaluated for early blight resistance in 1995 and 1996 in a randomized complete block design in Pennsylvania. Broad-sense heritability for early blight resistance among the open-pollinated4×-2× hybrids which were originally selected for horticultural characteristics was 0.91 with a 95% confidence interval of 0.80, 0.94. There were significant differences among female and male parents for area under the disease progress curve, indicating the importance of general combining ability for early blight resistance in this germplasm. The female x male source of variation was not significant, indicating that specific combining ability was not important. The greatest number of resistant progeny were observed in families where both parents were derived from the early blight resistant population; however, at least one highly resistant progeny was produced in all families. These results suggest that the early blight resistance in these clones can be readily incorporated into the commercial tetraploid breeding population.