Observations and thoughts on resistance of corn to Ustilago maydis

Transcription

1 Observations and thoughts on resistance of corn to Ustilago maydis Snook Pataky Department of Crop Sciences University of Illinois

2 Two paths of investigation screen sweet corn for resistance to smut produce cuitlacoche

3 Disease cycle - common smut Local infection of meristematic tissues - galls

4 Leaf Stalk axillary buds Tassel Ears Kernels

5 Ear Kernel galls

6 Host resistance earliest inbreds from OP cultivars had noticeably different smut reactions 1. Inbred lines with many galls or few galls (susceptible and resistant) 2. Inbred lines with galls on specific plant tissues (stalks, tassels, leaves, ears)

7 Genetic studies: inheritance of resistance Pathogenesis studies: mechanisms of resistance

8 Host resistance inbred lines can be produced easily with every degree of resistance to smut. 2. Further studies are necessary before determining how many factors are involved. 3. Little is known about the basic nature of resistance of corn to smut. J.J. Christensen, APS Monograph No. 2. Corn Smut

9 Inoculation method 1987 KJ Leonard, RP Thakur Injecting sporidia into stalks galls formed on various plant tissues in association with time of inoculation - leaves - axillary buds (stalk) - tassels - ear shoots (cob) kernel galls were NOT induced by stalk inoculation lack of correlation between hybrid response to greenhouse inoculation and natural infection in field trials Thakur, Leonard, Pataky. Plant Dis. 73: , 1989

10 Screen reactions sweet corn for formation of kernel galls various inoculation techniques teliospore, sporidia inocula sandblasting Wounding silks and spraying inocula in wounds

11 Injecting sporidial suspensions into silk channels reliably produced kernel galls Zimmerman & Pataky, Phyto. 82:995, 1992

12 silk channel inoculation

13 cuitlacoche

14 Screen sweet corn for resistance to common smut Sweet corn hybrid disease nursery silk channel inoculation (2 or 3 reps) 2- to 4-days past mid-silk stage natural infection (1 or 2 reps) hybrids hybrids hybrids Mike Kerns Claude Nankam Pataky, Kerns, Nankam. Phytopathology 85: , 1995

15 1992 n 345 mean 34% sd 20% range 0-96% LSD 17% Range of reactions incidence of infected ears severity of kernel infection 1993 n 372 mean 20% sd 13% range 0-80% LSD 14% 1994 n 367 mean 33% sd 17% range 0-91% LSD 16%

16 Reaction in year 2 Inconsistent between years Reaction in year 1 R-MR M MS-S R-MR M MS-S Pataky, Kerns, Nankam. Phytopathology 85: , 1995

17 1992 n 345 mean 34% sd 20% range 0-96% LSD 17% Separating something?? NOT - variation among hybrids for reactions to U. maydis 1993 n 372 mean 20% sd 13% range 0-80% LSD 14% 1994 n 367 mean 33% sd 17% range 0-91% LSD 16%

18 Sources of variation in silk channel inoculation variation among people inocula concentration du Toit, Pataky. Plant Disease 83: , 1999 Lindsey du Toit pollination and silk maturity du Toit, Pataky. Plant Disease 83: , 1999

19 Infection of kernels is affected by silk age and pollination silk age kernel galls decreased with silk age pollination uncovered silks - fewer galls covered silks (non-pollinated) receptive to infection for a longer period du Toit, Pataky. Plant Disease 83: , 1999

20 Pollination decreases kernel smut

21 Karen Snetselaar St. Joseph University, Philadelphia Infection of maize stigmas by Ustilago maydis: light and electron microscopy. Phytopathology 83: , teliospores germinate sporidia bud sporidia mate appressoria teliospores form

22 Pollination can protect ovaries from infection by U. maydis Infection hyphae Abscission of silk of fertilized ovary Snetselaar et al., Canadian J. Botany 79: , 2001

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24 No endosperm Gall - pericarp

25 Conflicting reports about smut-conducive environments hot, dry, drought conditions tassels burn out - no pollen when last silks emerge unpollinated silks at tip of ear rainy weather poor pollen shed sporidia disseminated

26 Variation among plants Silks 1 or 2 days No silks -1 to -3 days

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28 Does silk abcission differ between resistance and susceptible hybrids

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30 Percentage of silks attached. Rapidity of silk abcission GG3 smut susceptible GG46 smut resistant day difference Days after silk emergence Pataky & Richter. HortScience 42: , 2007

31 Resistance to kernel galls Combination of traits affecting silk dynamics and pollination rapidity of silk abcission synchrony between pollen production and silk emergence production of pollen under adverse conditions rainy weather, damp tassels; heat, drought stress wimpy males increased smut susceptibility (kernel galls) uniformity and time period of silk emergence silk dynamics

32 Resistance to kernel galls

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34 Marion Griffiths Assistant Pathologist Office of Crops and Diseases Bureau of Plant Industry USDA Smut susceptibility of naturally resistant corn when artificially inoculated J. Agr. Res 36:77-89 C. H. Kyle s resistant inbred lines needle inoculation

35 Mechanisms of resistance

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37 Different diseases

38 Resistance to U. maydis

39 Questions?