Additional physiological races of coffee leaf rust (Hemileia vastatrix) identified in Kenya

Abstract

Coffee leaf rust (CLR), caused by the fungus Hemileia vastatrix, is among the most important diseases affecting coffee all over the world. In Kenya, it is currently the second most important disease, and breeding coffee to obtain new resistant cultivars has been a priority. Over time, new rust pathogenic races able to infect hitherto resistant coffee genotypes have been registered. To date, 49 races of the pathogen have been characterized all over the world. The most recent races to be characterized are able to infect derivatives of Timor Hybrid (HDT), which is a major source of resistance in breeding programs. This work aimed to identify new races of the pathogen in Kenya, emphasizing infected leaves sampled from CLR resistant varieties and breeding lines collected from two sites (Ruiru and Koru). Twenty-four samples were characterized, out of which 22 samples corresponded to new races of the pathogen. A total of six new races (III, XVII, XXIII, XXXVI, XLI and XLII) were characterized, revealing three new virulence genes (v 1 , v 7 , v 8 ) and possibly a fourth virulence gene, the v 9 . This finding represents a serious threat to coffee production and also a challenge to coffee breeding programs that are in progress in Kenya.

High throughput transcriptome analysis of coffee reveals prehaustorial resistance in response to Hemileia vastatrix infection

“…The H. vastatrix races recently discovered have been able to infect derivatives of Híbrido de Timor (HdT), a natural hybrid originated from C. arabica and C. canephora crossing (Bettencourt 1973;Rodrigues et al 2004). HdT is the main source of resistance used in breeding programs throughout the world (Gichuru et al 2012;Zambolim 2016). The presence of such rust virulent races in the field represents a serious risk to coffee production worldwide.…”

Structural and functional analysis of genes with potential involvement in resistance to coffee leaf rust: a functional marker based approach

“…Despite the release of some resistant coffee cultivars in recent years, coffee rust continues to adversely affect coffee production and undermines the incomes of many households [2]. To date, at least 49 characterized physiological races of H. vastatrix have been reported [2, 3]. The consistent emergence of new races and the sporadic outbreaks of this disease have imposed challenges in resistance breeding.…”

“…Despite the partial sequencing and annotation of several disease resistance genes in Arabica coffee [20], completely sequenced and characterized candidate genes are not yet readily available. Resistance to rust is conferred by nine major genes (S H 1-9) and the corresponding v 1-9 pathogen factors are known for long in the coffee rust pathosystem [3, 21]. Nonetheless, molecular and functional characterization of any of the S H genes and the associated regulatory elements is entirely obscure, yet holds immense potential in changing the perspective of rust resistance breeding.…”

New coffee (Coffea arabica) genotypes derived from Coffea canephora exhibiting high levels of resistance to leaf rust and Ceratocystis canker

“…At least 49 rust races have been identified in coffee using a set of more than 40 coffee differentials, including the two commercial species cultivated in the world: Coffea arabica L. (tetraploid 2n=4x= 44) and C. canephora Pierre: A. Froehner (diploid 2n=2x=22) (Varzea & Marques, 2005;Gichuru et al, 2012). The pathogen H. vastatrix has (with various periods of delay), followed the spread of C. arabica around the world.…”

“…Despite the success of CLR breeding programs, there is evidence that some improved commercial varieties derived from TH have lost their resistance due to the possible emergence of new virulent races of the pathogen (Várzea & Marques, 2005;Prakash et al, 2005;Alvarado, 2005, Gichuru, et al, 2012. Variability in virulence of the pathogen could be due to natural mutation processes, but it could also arise from other mechanisms such as cryptic sex, a hidden sexual reproduction of the pathogen (Carvalho et al, 2011).…”