Viabilitas dan Virulensi Fusarium oxysporum f. sp. cubense yang Dipreservasi dengan Liofilisasi

Wilt disease caused by Fusarium oxysporum f. sp. cubense (Foc) is still pose as constraint to banana production all over the world. The objective of this research was to examine the viability and virulence of Foc isolates which had been preserved with lyophilization for 18 years. The experiment used 19 isolates of Foc, which were Pekulo, Sukorejo, Kali Sepanjang, Kalibaru, Purwojoyo, Prembun, Mulyosari, Sidogede, Sidatan, Kemiri, Juwangen, A-17, A-11, PS-5, B4-3-1, Fo2.16.16., PS-10, A-2, and Irja. The results showed that 12 isolates could grow well on PDA medium, namely Pekulo, Sukorejo, Kali Sepanjang, Kalibaru, Purwojoyo, Prembun, Mulyosari, Sidatan, Juwangen, PS-5, B4-3-1, and Fo2.16.16. Meanwhile, seven isolates (Sidogede, Kemiri, A-17, A-11, PS-10, A-2, and Irja) could not grow or develop on PDA medium. The result of pathogenicity test showed that six tested Foc isolates had very high virulences, with disease severity index of about 2.14–2.71. Other three isolates revealed high virulences with disease severity index around 2.01–2.07. Meanwhile, another three less virulent isolates demonstrated disease severity index in the range of 1.39–1.67. Intisari Penyakit layu yang disebabkan oleh jamur Fusarium oxysporum f. sp.cubense (Foc) masih menjadi kendala dalam produksi pisang di seluruh dunia. Tujuan dari penelitian ini adalah untuk menguji viabilitas dan virulensi isolat Foc yang telah dipreservasi dengan liofilisasi selama 18 tahun. Penelitian menggunakan 19 isolat Foc yaitu Pekulo, Sukorejo, Kali Sepanjang, Kalibaru, Purwojoyo, Prembun, Mulyosari, Sidogede, Sidatan, Kemiri, Juwangen, A-17, A-11, PS-5, B4-3-1, Fo2.16.16., PS-10, A-2, dan Irja. Hasil penelitian menunjukkan bahwa 12 isolat Foc mampu tumbuh dengan baik pada medium PDA yaitu Pekulo, Sukorejo, Kali Sepanjang, Kalibaru, Purwojoyo, Prembun, Mulyosari, Sidatan, Juwangen, PS-5, B4-3-1, dan Fo2.16.16. 7 isolat tidak mampu tumbuh pada medium PDA yaitu Sidogede, Kemiri, A-17, A-11, PS-10, A-2, dan Irja. Enam isolat Foc yang diuji memiliki virulensi sangat tinggi dengan indeks keparahan penyakit berkisar antara 2,14–2,71. Tiga isolat yang lain memiliki virulensi tinggi dengan indeks keparahan penyakit berkisar antara 2,01–2,07. Sedangkan 3 isolat lainnya memiliki virulensi yang lebih rendah dengan indeks keparahan penyakit berkisar antara 1,39–1,67.

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Greenhouse Cucumber Cultivars Differ in Susceptibility to Fusarium Root and Stem Rot

HortTechnology ◽

10.21273/horttech.14.2.0240 ◽

2004 ◽

Vol 14 (2) ◽

pp. 240-242 ◽

Cited By ~ 6

Author(s):

Steve Rose ◽

Zamir K. Punja

Keyword(s):

Fusarium Oxysporum ◽

Disease Severity ◽

Severity Index ◽

Stem Rot ◽

Disease Severity Index ◽

Plant Mortality ◽

Breeding Lines ◽

The Third ◽

Enhanced Resistance ◽

Greenhouse Cucumber

Eighteen cucumber (Cucumis sativus L.) cultivars (long English type) were screened for their susceptibility to fusarium root and stem rot caused by Fusarium oxysporum Schlechtend.: Fr. f.sp. radicis-cucumerinum D.J. Vakalounakis using seedlings at the third true-leaf stage. Roots were trimmed and dipped into a spore suspension (105 spores/mL) of the pathogen and the plants were re-potted. A disease severity index (DSI) was used to assess disease responses 4 or 8 weeks later based on plant mortality and the height of surviving plants compared to the noninoculated controls. `Sienna', `Amazing' and `Dominica' were most susceptible to infection and the resulting DSI values were significantly (P ≤ 0.05) higher compared to noninoculated control plants. The cultivars `Korinda', `Euphoria' and `Aviance' displayed significantly lower DSI values which were not significantly different from noninoculated control plants. The remaining 12 cultivars displayed DSI values which were intermediate between the above two classes of responses. The results from this study indicate there is the potential to identify and develop cultivars and breeding lines of greenhouse cucumbers with enhanced resistance to fusarium root and stem rot.

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Virulensi Isolat Fusarium oxysporum f. sp. cubense VCG 01213/16 pada Pisang Barangan dari Varietas Pisang dan Lokasi yang Berbeda

Jurnal Hortikultura ◽

10.21082/jhort.v21n2.2011.p145-151 ◽

2016 ◽

Vol 21 (2) ◽

pp. 145

Author(s):

Jumjunidang ◽

Catur Hermanto ◽

Riska

Keyword(s):

Fusarium Oxysporum ◽

Incubation Period ◽

Disease Severity ◽

Control Method ◽

Block Design ◽

Severity Index ◽

Disease Severity Index ◽

Tropical Fruit ◽

Randomized Block Design ◽

Tissue Culture Propagation

Analisis genetik isolat-isolat cendawan Fusarium oxysporum f. sp. cubense (Foc) VCG 01213/16 penyebab penyakit layu pada tanaman pisang menunjukkan adanya keragaman yang nyata. Penelitian bertujuan mempelajari keragaman virulensi isolat-isolat yang terkelompok dalam VCG 01213/16, berasal dari berbagai daerah dan varietas pisang yang berbeda. Penelitian dilakukan di Laboratorium Penyakit dan Rumah Kasa Balai Penelitian Tanaman Buah Tropika (Balitbu Tropika) Solok, dari bulan Maret sampai dengan Juni 2009. Rancangan yang digunakan ialah acak kelompok dengan 10 perlakuan dan tiga ulangan, masing-masing perlakuan terdiri atas 10 tanaman. Perlakuan terdiri atas 10 isolat Foc VCG 01213/16 yang berasal dari varietas pisang dan lokasi berbeda. Tanaman uji ialah benih pisang Barangan hasil perbanyakan kultur jaringan. Hasil penelitian menunjukkan bahwa terdapat keragaman virulensi 10 isolat Foc VCG 01213/16 yang dinilai dari perbedaan masa inkubasi, persentase serangan, dan indeks keparahan penyakit pada bonggol dan daun pisang Barangan. Sembilan isolat Foc yang diuji mempunyai virulensi yang tinggi. Masa inkubasi berkisar antara 13,98 dan 16,80 hari, persentase serangan 93,33-100%, dan indeks keparahan penyakit pada bonggol dan daun masing-masing berkisar 3,46-5,35 dan 4,68-5,41. Isolat Foc VCG 01213/16 yang berasal dari Jabung-Lampung Timur dan diisolasi dari pisang varietas Ambon Kuning (isolat F) menunjukkan virulensi yang relatif lebih rendah dibanding sembilan isolat Foc lainnya dengan masa inkubasi 30,27 hari, indeks keparahan penyakit pada bonggol dan daun masing-masing sebesar 2,14 dan 3,76. Hasil penelitian ini bermanfaat dalam memberikan informasi tentang biologi F. oxysporum f. sp. cubense sebagai dasar untuk penyusunan teknik pengendalian yang tepat. Genetic analysis of isolates of the Fusarium oxysporum f. sp. cubense (Foc) that are grouped in VCG 01213/16, as the causal agent of wilt disease in banana plants showed a considerable variation. This research aimed to study the variation in virulence of isolates that are grouped in VCG 01213/16 from different varieties of banana and regions. The study was conducted in the Protection Laboratory and the Screenhouse of Indonesian Tropical Fruit Research Institute (ITFRI) Solok, from March to June 2009. A randomized block design was used in this research with 10 treatments and three replications. Each treatments consisted of 10 banana plants. The treatment was 10 Foc isolates belonging to VCG 01213/16 originating from different varieties of banana and locations. Barangan plantlets produced from tissue culture propagation were used as the planting material. The results showed that there were high variations in virulence among 10 Foc isolates in VCG 01213/16 based on variables of the incubation period, percentage of wilt, and disease severity index on corm and leaves of Barangan variety. Nine of the 10 Foc isolates tested were highly virulent isolates. The incubation period ranged from 13.98 to 16.80 days, the percentage of wilt from 93.33 to 100%, and the disease severity index of corm and leaves ranged from 3.46 to 5.35 and from 4.68 to 5.41, respectively. The Foc VCG 01213/16 isolates originated from Jabung, East Lampung and from Ambon Kuning variety (isolate F) shown relatively low virulence than others isolates that the incubation period was 30.27 days and the disease severity index on the corm and leaves was 2.14 and 3.76, respectively. This result provides useful information on biology of F. oxysprum f. sp. cubense to find out the best control method of the pathogen.

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Indonesian red chilli (Capsicum annuum L.) capsaicin and its correlation with their responses to pathogenic Fusarium oxysporum

NICHE Journal of Tropical Biology ◽

10.14710/niche.1.2.7-12 ◽

2018 ◽

Vol 1 (2) ◽

pp. 7

Author(s):

Rejeki Siti Ferniah ◽

Sri Pujiyanto ◽

Hermin Pancasakti Kusumaningrum

Keyword(s):

Disease Resistance ◽

Fusarium Oxysporum ◽

Disease Severity ◽

Food Industry ◽

Regression Coefficient ◽

Severity Index ◽

Post Inoculation ◽

Disease Severity Index ◽

Commercial Crop

Red chili is a commercial crop for the food industry in Indonesia. There are some categories of red chili based on their pungency. The hot chili usually has more capsaicin than the sweet chili. Some cultivars may have more resistance to pathogen infection than the others. This research aimed to analyze the disease resistance of red chili cultivars from Indonesia against pathogenic Fusariumoxysporum and the correlation with capsaicin contents. Disease resistance was examined by determination of the Disease Severity Index (DSI) 15 dpi (days post inoculation). The correlation was analyzed by the regression coefficient. The result showed that the most resistance cultivar against F. oxysporum was Branang, while Lembang-1displayed the contrary. There was not a correlation of capsaicin content with the chili resistance to F. oxysporum.

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Biological Management of Banana Fusarium Wilt Caused by Fusarium oxysporum f. sp. cubense Tropical Race 4 Using Antagonistic Fungal Isolate CSR-T-3 (Trichoderma reesei)

Frontiers in Microbiology ◽

10.3389/fmicb.2020.595845 ◽

2020 ◽

Vol 11 ◽

Author(s):

Thukkaram Damodaran ◽

Shailendra Rajan ◽

Manoharan Muthukumar ◽

Ram Gopal ◽

Kavita Yadav ◽

...

Keyword(s):

Gene Expression ◽

Biological Control ◽

Fusarium Oxysporum ◽

Trichoderma Reesei ◽

Disease Severity ◽

Expression Analysis ◽

Gene Expression Analysis ◽

Severity Index ◽

Disease Severity Index ◽

Race 4

Fusarium wilt in bananas is one of the most devastating diseases that poses a serious threat to the banana industry globally. With no effective control measures available to date, biological control has been explored to restrict the spread and manage the outbreak. We studied the effective biological control potential of different Trichoderma spp. in the management of Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4). Expression of the defense related genes and metabolites in banana plants inoculated with Foc TR4 and treated with effective Trichoderma sp interactions were also studied. The in vitro growth inhibition of Foc TR4 by Trichoderma reesei isolate CSR-T-3 was 85.19% indicating a higher antagonistic potential than other Trichoderma isolates used in the study. Further, in in vivo assays, the banana plants treated with the isolate CSR-T-3 T. reesei had a significant reduction in the disease severity index (0.75) and also had increased phenological indices with respect to Foc TR4 treated plants. Enhanced activity of defense enzymes, such as β-1, 3-glucanase, peroxidase, chitinase, polyphenol oxidase, and phenylalanine ammonia lyase with higher phenol contents were found in the Trichoderma isolate CSR-T-3 treated banana plants challenge-inoculated with Foc TR4. Fusarium toxins, such as fusaristatin A, fusarin C, chlamydosporal, and beauveric acid were identified by LC-MS in Foc TR4-infected banana plants while high intensity production of antifungal compounds, such as ß-caryophyllene, catechin-o-gallate, soyasapogenol rhamnosyl glucoronide, peptaibols, fenigycin, iturin C19, anthocyanin, and gallocatechin-o-gallate were detected in T. reesei isolate CSR-T-3 treated plants previously inoculated with Foc TR4. Gene expression analysis indicated the upregulation of TrCBH1/TrCBH2, TrXYL1, TrEGL1, TrTMK1, TrTGA1, and TrVEL1 genes in CSR-T-3 treatment. LC-MS and gene expression analysis could ascertain the upregulation of genes involved in mycoparasitism and the signal transduction pathway leading to secondary metabolite production under CSR-T-3 treatment. The plants in the field study showed a reduced disease severity index (1.14) with high phenological growth and yield indices when treated with T. reesei isolate CSR-T-3 formulation. We report here an effective biocontrol-based management technological transformation from lab to the field for successful control of Fusarium wilt disease caused by Foc TR4 in bananas.

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EVALUATION OF NONIONIC SURFACTANTS FOR CONTROL OF CLUBROOT OF CABBAGE USING BAREROOT AND PLUG TRANSPLANTS OF TWO CULTIVARS

HortScience ◽

10.21273/hortsci.27.6.607b ◽

1992 ◽

Vol 27 (6) ◽

pp. 607b-607

Author(s):

W. Tietjen ◽

P.J. Nitzsche ◽

W.P. Cowgill ◽

M.H. Maletta ◽

S.A. Johnston

Keyword(s):

Brassica Oleracea ◽

Disease Severity ◽

Nonionic Surfactants ◽

Plasmodiophora Brassicae ◽

Severity Index ◽

Effective Control ◽

Disease Severity Index

`Market Prize' and `Bravo' cabbage (Brassica oleracea Var. capitata L.), transplanted as peat plug and bareroot plants into a field naturally infested with Plasmodiophora brassicae, Woronin, were treated immediately after planting with a liquid or a granular surfactant. APSA 80™, applied in transplant water, significantly reduced percent clubbing and disease severity index (DSI) compared to control treatments. Miller Soil Surfactant Granular™ did not significantly reduce percent clubbing or DSI. There was a significant effect of cultivar on percent clubbing and DSI. There was no significant effect of transplant type on percent clubbing or DSI. This year's study culminates five years of investigation of surfactants for clubroot control. Specific surfactants have proven to be an effective control of clubroot in cabbage. Chemical names used: nonylphenoxypolyethoxyethanol (APSA 80™); alpha-alkanoic-hydro omega-hydroxy poly (oxyethylene) (Miller Soil Surfactant Granular™).

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Summer Heat and Low Soil Organic Matter Influence Severity of Hazelnut Cytospora Canker

Phytopathology ◽

10.1094/phyto-05-13-0136-r ◽

2014 ◽

Vol 104 (4) ◽

pp. 387-395 ◽

Cited By ~ 4

Author(s):

Jay Ram Lamichhane ◽

Alfredo Fabi ◽

Leonardo Varvaro

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Disease Severity ◽

Severity Index ◽

Stress Factors ◽

Disease Severity Index ◽

Positive Correlation ◽

Summer Heat ◽

Production Areas ◽

Cytospora Canker

Cytospora canker, caused by the fungus Cytospora corylicola, is present in hazelnut production areas worldwide. The disease is widespread throughout the main production areas of Italy. The causal agent is considered to be a secondary invader of damaged tissue that attacks mainly stressed plants. However, little is known of disease severity and stress factors that predispose plants to infection. In particular, the role of pedoclimatic factors was investigated. Direct survey indicated that disease severity varied across several study sites. Geostatistics showed a strong positive correlation between disease severity index and summer heat (r = 0.80 and 0.91 for July and August, respectively) and strong negative correlation between disease severity index and soil organic matter (r = –0.78). A moderate positive correlation between disease severity index and magnesium/potassium ratio (r = 0.58) and moderate negative correlations between disease severity index and total soil nitrogen (r = –0.53), thermal shock (r = –0.46), and rainfall (r = –0.53) were determined. No significant correlation between disease severity index and soil aluminum (r = –0.35), soil pH (r = –0.01), and plant age (r = –0.38) was found.

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The relationship between SPAD chlorophyll and disease severity index in Ganoderma-infected oil palm seedlings

Journal of the Bangladesh Agricultural University ◽

10.3329/jbau.v17i3.43211 ◽

2019 ◽

Vol 17 (3) ◽

pp. 355-358 ◽

Cited By ~ 1

Author(s):

M.R.M. Rakib ◽

A.H. Borhan ◽

A.N. Jawahir

Keyword(s):

Chlorophyll Content ◽

Disease Severity ◽

Oil Palm ◽

Single Photon ◽

Linear Trend ◽

Severity Index ◽

Quadratic Model ◽

Wood Block ◽

Disease Severity Index ◽

The Relationship

Establishment of disease in oil palm seedlings through artificial inoculation of Ganoderma are widely used for studies of various aspects of plant pathology, including epidemiology, etiology, disease resistance, host-parasite interaction and disease control. The estimation of chlorophyll content in the infected seedlings possibly could provide a good indicator for degree of disease or infection, and changes during pathogenesis. Thus, the objective of this study was to evaluate the relationship between disease severity index (DSI) and chlorophyll content in Ganoderma infected oil palm seedlings. Three-month-old oil palm seedlings were infected with Ganoderma inoculum on rubber wood block (RWB), where 44 isolates of Ganoderma were tested. Disease severity index (DSI) and chlorophyll content using a single-photon avalanche diode (SPAD) meter were recorded at 4 weeks interval for a period of 24 weeks after inoculation (WAI). Pearson's correlation analysis and regression analysis were performed to evaluate the relationship between the variables. It was found that the relationship between DSI and SPAD chlorophyll value was inversely proportional (R = -0.92) in a linear trend (R2 = 0.85). Furthermore, the increasing trend of the DSI across the weeks were fitted in a quadratic model (R2 = 0.99). In contrast, the SPAD chlorophyll value declined in a linear trend (R2 = 0.98). The SPAD chlorophyll value could be considered as a better alternative over the DSI as the SPAD chlorophyll value was strongly related to DSI, as well as able to detect physiological changes in the infected oil palm seedlings at the early stages of pathogenesis. J Bangladesh Agril Univ 17(3): 355–358, 2019

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Variation patterns within 153 flax (Linum usitatissimum L.) genebank accessions based on evaluation for resistance to fusarium wilt, anthracnose and pasmo

Plant Genetic Resources ◽

10.1017/s1479262108913897 ◽

2008 ◽

Vol 6 (1) ◽

pp. 22-32 ◽

Cited By ~ 11

Author(s):

Axel Diederichsen ◽

Tatiana A. Rozhmina ◽

Ljudmilla P. Kudrjavceva

Keyword(s):

Disease Severity ◽

Fusarium Wilt ◽

Linum Usitatissimum ◽

Indian Subcontinent ◽

Severity Index ◽

Disease Severity Index ◽

Fibre Flax ◽

Linum Usitatissimum L ◽

Average Resistance ◽

Variation Patterns

Germplasm of 153 flax (Linum usitatissimum) accessions from 24 countries held at Plant Gene Resources of Canada (PGRC) was evaluated for resistance to fusarium wilt (Fusarium oxysporum), anthracnose (Colletotrichum lini) and pasmo (Septoria linicola). The screening was conducted at the All-Russian Flax Research Institute (VNIIL) at Torzhok, Russia, over 3 years for fusarium wilt and anthracnose, and over 2 years for pasmo. A disease severity index ranging from 0% (no infection) to 100% (heavy infection) was calculated based on observations after artificial inoculation with the pathogens in the greenhouse (fusarium wilt) or in field nurseries (anthracnose and pasmo). The average disease severity index for fusarium wilt was 56.6 ± 34.4% (range 0–100.0%), for anthracnose 59.8 ± 8.1% (range 43.8–83.9%) and for pasmo 74.2 ± 11.8% (range 27.3–100.0%). The variation of disease severity indices among the years and within each accession was highest for fusarium wilt. Higher than average resistance for all three diseases was found in accessions from East Asia, while germplasm from the Indian subcontinent showed considerably lower than average resistance. Germplasm from North America and South America (mostly linseed) displayed above average resistance to fusarium wilt, while European accessions (mostly fibre flax) showed lower than average resistance to this disease. The different resistance levels reflected the improvements made by plant breeding and differences in the environments under which the germplasm accessions evolved. Accessions with potential use in linseed and fibre flax breeding were identified.

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Case Study of an Epidemiological Approach Dissecting Historical Soybean Sclerotinia Stem Rot Observations and Identifying Environmental Predictors of Epidemics and Yield Loss

Phytopathology ◽

10.1094/phyto-12-16-0446-r ◽

2018 ◽

Vol 108 (4) ◽

pp. 469-478 ◽

Cited By ~ 10

Author(s):

Mamadou L. Fall ◽

John F. Boyse ◽

Dechun Wang ◽

Jaime F. Willbur ◽

Damon L. Smith ◽

...

Keyword(s):

Disease Severity ◽

Yield Loss ◽

Historical Data ◽

Severity Index ◽

Stem Rot ◽

Total Precipitation ◽

Disease Severity Index ◽

Sclerotinia Stem Rot ◽

Environmental Predictors ◽

Epidemiological Approach

Sclerotinia sclerotiorum is a significant threat to soybean production worldwide. In this study, an epidemiological approach was used to examine 11 years of historical data from a soybean management performance trial in order to advance our understanding of Sclerotinia stem rot (SSR) development and to identify environmental predictors of SSR epidemics and associated yield losses. Recursive partitioning analysis suggested that average air temperature and total precipitation in July were the most significant variables associated with disease severity. High levels of SSR disease severity index were observed when the average temperature in July was below 19.5°C and total precipitation in July was moderate, between 20 and 108.5 mm. A biphasic sigmoidal curve accurately described the relationship between SSR disease severity index (DSI) and yield, with a DSI threshold of 22, below which minimal yield loss was observed. A 10% increase in the DSI, from 22.0 to 24.2, led to an 11% decrease in yield, from 3,308.14 to 2,951.29 kg/ha. Also, a yield threshold (3,353 kg/ha) that was higher than the annual U.S. average soybean yield (3,039.7 kg/ha) was suggested as an expected yield under low or no SSR pressure in the U.S. Midwest. These thresholds can allow soybean stakeholders to assess the value of disease control and establish an SSR baseline for cost-effective management to protect yields. Because S. sclerotiorum has more than 400 plant host species, and because having quantitative information concerning crop losses is crucial for decision making, this study shows the usefulness of historical data on SSR and, hence, can serve as a model in other SSR pathosystems (canola, dry bean, potato, pea, and so on).

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Inheritance of resistance to Mal de Río Cuarto (MRC) disease in Zea mays (L.)

The Journal of Agricultural Science ◽

10.1017/s0021859602002241 ◽

2002 ◽

Vol 139 (1) ◽

pp. 47-53 ◽

Cited By ~ 7

Author(s):

M. A. DI RENZO ◽

N. C. BONAMICO ◽

D. D. DÍAZ ◽

J. C. SALERNO ◽

M. M. IBAÑEZ ◽

...

Keyword(s):

Zea Mays ◽

Plant Height ◽

Disease Severity ◽

Agronomic Traits ◽

Severity Index ◽

Point Estimate ◽

Environment Interaction ◽

Disease Severity Index ◽

Evaluation Activity ◽

Genotype Environment Interaction

No genetic estimates for resistance to Mal de Río Cuarto (MRC) disease in Zea mays (L.) are currently available in the literature. Therefore, the objectives of this investigation were (i) to estimate the variance and heritability of partial resistance to MRC disease and of other agronomic traits from maize families and (ii) to examine associations among MRC disease severity values across different environments and between MRC and other agronomic traits. These estimations, obtained in an endemic area, could contribute to the design of efficient enhancement programmes and evaluation activity for the improvement of MRC resistance. The research was conducted by testing 227 F3 derived-lines from a cross between a susceptible dent line, Mo17, and a partially resistant flint line, BLS14, for MRC disease at two Río Cuarto locations in each of 2 years. The resistance of the lines, measured with a disease severity index (DSI), was normally distributed across environments. Genotypic variances were highly significant on all scoring environments. Estimates of genotype–environment interaction were also significant, suggesting that certain genotypes have little stability over different environments. For disease severity index all estimates demonstrated moderate heritabilities ranging from 0.44 to 0.56 and were similar when based on individual environments or across environment. Confidence interval widths ranged from 34.88 to 50.30% as large as the heritability point estimate. The correlations between environments were small enough to indicate that families did not rank similarly in individual environments for MRC resistance. Disease severity index correlated significantly (P<0.01) with plant height, leaf surface, leaf border, leaf length and tassel type. Heritability estimates for plant height and tassel type were 0.48 and 0.38 respectively and for the various leaf traits heritability values were very low. On the basis of the substantial genotype–environment interaction and the little association between DSI values in the different environments, selection for an increased resistance to MRC disease would require evaluation of germplasm across multiple years and locations. Tassel type would be a useful predictor of DSI and can be used effectively to improve screening procedures.

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