Background

Black shank, caused by the Oomycete Phytophthora parasitica var. nicotianae is a widespread and destructive disease of tobacco (Nicotiana tabacum) that affects all types of cultivated tobacco worldwide with losses in individual fields reaching 100 %. Populations of P. nicotianae are variable around the world and four different races (race 0, 1, 2 and 3) have been reported to occur on tobacco. The most effective strategy for reducing economic losses from this pathogen is development and use of resistant tobacco varieties. However, the different P. nicotianae races are defined by their ability to infect various cultivars with different resistance genes. From time to time the rapid emergence of new races and shifts in field population race compositions frequently renders some resistant varieties susceptible to the disease, leading to breeders searching for new sources of resistance.

There have been reports of suspected shifts in the race composition of the pathogen in some tobacco producing countries resulting in some previously resistant varieties succumbing to the disease. This development has necessitated the CORESTA Black Shank Collaborative Study, the objectives of which are for participants to establish the race composition of Phytophthora parasitica var. nicotianae infecting tobacco in their respective countries and to evaluate available black shank resistant tobacco varieties for their susceptibility to the disease. Additionally, there is a need to determine conclusively that all black shank related reports received are due to Phytophthora parasitica var. nicotianae and not Fusarium, a fungal pathogen whose disease symptoms are very similar and for which misdiagnosis is common.

Purpose

This collaborative study is not a new project, as there was previously a CORESTA Black Shank Collaborative Study conducted and then terminated many years ago. However, it was considered necessary to conduct this study again because the Phytophthora parasitica var. nicotianae race composition has changed in many places. The various breeding programmes in several tobacco growing countries have also developed newer, more resistant varieties and there is a need to establish the relative resistances of these varieties to the various races in different locations. Additionally, there have been reports of misdiagnosis of Fusarium wilt as black shank and there is a need to establish for sure that all losses being attributed to P. parasitica var. nicotianae are accurate.

In January 2024, the initial objectives of the Sub-Group were revised in order to better reflect the work of the group as it has evolved over time.

Leaders:

Coordinator: Yuan Zeng, Virginia Tech, USA
Secretary: Daisy Ahumada, North Carolina State University, USA

Varieties

A request has been sent out to participants who can contribute some seed of resistant varieties for testing in the trials. However, in the absence of these, participants are encouraged to test their own seed varieties

Activities

1. Engaging more participants
2. Establishing the range of resistant varieties that participants can share
3. Sourcing of seed of resistant varieties for distribution to participants

Next Steps

1. Standardisation of protocols
2. Implementation of field trials
3. Working out the logistics of seed exchange among participants.

Updated January 2024