Resistance against Fusarium root rot of dry bean
March 07, 2008
Rubella Goswami, Carl Bradley, and Jack Rasmussen
Department of Plant Pathology
North Dakota State University
Dr. Bradley is now at the University of Illinois
Objectives: The objective of this research is to assist the development of dry bean germplasm and resistance to Fusarium root rot for the Northarvest production area by a) screening germplasm for root rot resistance, and (b) conducting experiments to determine the genetics of resistance to Fusarium root rot in Vax 3.
Progress: In previous work supported by Northarvest, we developed an inoculation technique, termed the layered inoculum method, as a greenhouse and laboratory tool to effectively evaluate dry bean reaction to Fusarium root rot. This method was used to assess eleven dry bean cultivars, representing different market classes, for their level of resistance to Fusarium root rot in field (Fargo, ND and Park Rapids and Perham, MN) and greenhouse trials. As expected, dark red kidneys (cultivars Montcalm and Red Hawk) were among the most susceptible. By comparison, Vax 3 had good resistance suggesting that this variety may be a good source of genetic resistance to Fusarium root rot. For purposes of elucidating the genetics of resistance, crosses were made between Vax 3 (resistant parent) and the dark red kidney variety Red Hawk by the breeding group. Red Hawk is highly susceptible to this disease, despite many other desirable agronomic characteristics (yield, quality, and so forth). F1 progeny were tested by us and found to be disease resistant. This implicates but does not by itself prove that resistance may be genetically dominant. [This would be good for the breeding program because resistance conditioned by dominant gene(s) is easier to work with]. Proof of genetic dominance requires analysis of F2 and F3 populations, which would segregate for susceptibility and resistance. Those populations have been developed and screened in the laboratory and green house. Progeny have been forwarded to the F6 generation and the recombinant inbred lines are currently being evaluated for resistance to identify potential parents for the breeding program. These populations will subsequently be used for molecular analysis to try to identify markers that can be linked to root rot resistance and used for marker assisted selection of breeding lines.
In other experiments, we investigated the ability of Fusarium graminearum, previously known to cause head blight of wheat and barley, to cause root rot in dry bean cultivars. We used greenhouse experiments to determine the reaction of dry bean genotypes from six different market classes to F. graminearum. VAX 3, Eclipse, and T-39 were found to be more resistant to this pathogen as well when compared to Rojo Chiquito, Red Hawk, Montcalm and other genotypes, including two pinto beans. These results suggest that dry bean genotypes with susceptibility to F. solani may have susceptibility to F. graminearum and those with resistance to one pathogen may have resistance to the other, at least under greenhouse conditions. We emphasize that the importance of F. graminearum as a root rot pathogen of dry bean in commercial fields was not investigated in these experiments and needs to be a topic for future research.
Figure 1: A-D Greenhouse evaluations: (A) Susceptible root rot reaction of "Rojo Chiquoto" to F. solani f sp phaseoli (B) Susceptible reaction of "Rojo Chiquoto to F. graminearum (C) Resistance type reaction of T-39 to F. solani f sp. phaseoli (D) Resistance type reaction of T-39 to F. graminearum.