# Presentation: 003357

## Identification, Mefenoxam Sensitivity, and Mating Type of Phytophthora spp. attacking Floriculture Crops in North Carolina 

**Identification, Mefenoxam Sensitivity, and Mating Type of *****Phytophthora***** spp. attacking Floriculture Crops in North Carolina**

**Jaesoon Hwang and D. M. Benson**

## Floriculture crops production in North Carolina

- Wholesale value of $161.4 million in 2001 (8th in the nation)
- 335 growers, 17.9 million square feet of covered area
- Phytophthora diseases - one of the major problems, potential movement within state/among states, 21% of growers using mefenoxam

## Objectives of project

- Identify *Phytophthora* spp. causing blight, crown rot, and root rot on floricuture crops
- Characterize isolates for sensitivity to mefenoxam
- Determine mating type of isolates

## Isolate collection

- 61 wholesale growers listed in NCCFGA
-    -29 operations visited (>1/4 to 65 acres)

## Isolate collection

- 46 plant species sampled
- 	African violet, artemisia, begonia, campanula, carnation, chrysanthemum, cladium, cyclamen, dahlia, Dusty Miller, English ivy, fuchsia, gardenia, garden sage, geranium, gerber, gloxinia, impatiens, lamb’s ear, lantana, lavender, lusianthus, marigold, miniature rose, New Guinea impatiens, oregano, pansy, pentas, petunia, plectranthus, poinsettia, portulaca, pothos, rhodochiton, rosemary, salvia, Scotch moss, snapdragon, syngonium, verbena, vinca, viola,

## Isolate collection

- Direct isolation from leaf, crown, and root using PAR/Hymexazol
- 14 groups, 486 isolates collected
- Isolate ; *Phytophthora* isolated from an individual plant
- Group ; Isolates collected from the same host at a given location

## Species identification

- Morphological & physiological characteristics
- 		Ho et al. 1995
- 		Waterhouse 1970

## Species identification

- PCR using ITS 4 and 5 primers & digestion with RsaI, MspI, HaeIII
- 		Ristaino et al. 1998

## PCR: Species identification

- P. palmivora

- P. nicotianae

- P. palmivora

- Cut with RsaI

## PCR: Species identification

- P. cryptogea

- P. drechsleri

- Cut with HaeIII

## Species identified by morphological & molecular (PCR) characteristics 

## A potential new Phytophthora species

- Isolated from English ivy at two locations
- Koch’s postulate completed
- Closely related to *P. tropicalis*
- 	- morphological characteristics
- 	- DNA sequence analysis

## Mefenoxam sensitivity

- 0, 1, 100 ppm (Subdue Maxx a.i.) corn meal agar plates
- - ; No growth
- 	+; 1-24%
- 	++; 25-49%
- 	+++; 50-74%
- 	++++; 75-100%

## Mefenoxam sensitivity

## Mefenoxam sensitivity at 100ppm

*P. cryptogea*
- 	- sensitive (-); 8%
- 	- intermediate (+~+++); 19%
- 	- resistant (++++); 73%* *
*P. nicotianae*
- 	- sensitive (-); 80%
- 	- resistant (++++); 20%
*P. palmivora*
- 	- sensitive (-); 100%

## Mating type determination

- Tester isolates
- 	*P. capsici*
-  	  OP97 (A1)
- 	  SP98 (A2)
- 	*P. nicotianae*
- 	  MLPT (A2)
- 	  FBPS (A1)

## Host/species/mating type

- UD ; Undetermined

## A1, A2 coexist in NC

*P. nicotianae*
- Potential spread & long-term survival of mefenoxam resistant isolates

## Homogeneity within a group

- 12 of 14 groups (host by location combinations)
- 	- Within a group, all isolates showed same level                                                                                                                                                                                                                of sensitivity to mefenoxam
- 	- Within a group, all isolates were same mating                                                                                                                                                                                                                 type
- 	- Originated from one source?

## Variations of mefenoxam sensitivity within a group

*P. cryptogea* from Dusty miller
*P. cryptogea* from gerber

## 2001 vs 2002

*P. nicotianae* from African violet collected at same location
- Homogeneous mating type and mefenoxam sensitivity over year
- 	- originated from same source?

## 2001 vs 2002

*P. cryptogea* from Dusty miller collected at same location
- Increased sensitivity to mefenoxam over year
- 	- originated from different source?
- 	- shift the other way?

## Comparison of Phytophthora in NC & MI (K. Lamour & M. Hausbeck) 

**North Carolina**
- Prevalent species
- 		*P. nicotianae*
- Overall mefenoxam resistant isolates
- 35%
- A1, A2 mating type
- coexist for *P. nicotianae*
- Homogeneity within a group
- Yes (for 12 of 14 groups)

**Michigan**
- 		*P. nicotianae*
- 8%
- coexist for *P. nicotianae*
- Yes (for all groups)

## Summary

*P. cryptogea, nicotianae, palmivora* isolated
- 35% of isolates were resistant to mefenoxam
- Homogeneity within a group
- 	- same origin
- Variations within a group / among groups
-   	- shift in progress
- 	- different origin
- Both mating type coexist for *P.nicotianae*
- A potential new species from English ivy

## Significance to the industry

- Diversity of *Phytophthora* spp. recovered
- 	- appropriate control strategies based on the                                                                                                                                                                                                                   biology of each species
- Multiple *Phytophthora* spp. may present in an operation
- 	- significance of population monitoring &                                                                                                                                                                                                                       chracterization

## Significance to the industry

- High percentage of mefenoxam resistant isolates
- 	- could result in fungicide failure
- 	- need to develop fungicide resistance                                                                                                                                                                                                                          management program
- 		new fungicides
- 		rotation of multiple fungicides
- 		evaluating cross-resistance with other fungicides

## Special thanks to

- Growers in North Carolina
- Luis Gomez
- Dr. Seong-Hwan Kim
- Dr. Kurt Lamour
- Dr. Jean B. Ristaino
- Dr. Brian E. Whipker
- NCSU Plant Disease & Insect Clinic