scholarly journals Modern Breeding Approaches for Durable Resistance Against the Parasitic Plant Striga

Afrika Focus ◽  
2019 ◽  
Vol 32 (2) ◽  
pp. 109-115
Author(s):  
Steven Runo
Keyword(s):  
Host Resistance ◽  
Chemical Cues ◽  
Smallholder Farmers ◽  
Durable Resistance ◽  
Resistance Breeding ◽  
New Paradigm ◽  
Severe Retardation ◽  
Modern Breeding ◽  
Great Danger ◽  
Durability Of Resistance

Crop losses caused by parasitic plants of the genus Striga pose a great danger to the livelihoods of millions of smallholder farmers in Africa. The parasite attaches to host crops and siphons nutrients leading to severe retardation and crop death. Controlling Striga is difficult because of the parasite’s ability to produce large amounts of seeds that can remain dormant in the soil for decades – only germinating in response to chemical cues (strigolactones) from the host. In recent years, breeding crops for host-based resistance has been prioritized. However, such programs have not taken into account Striga’s ability to overcome host resistance. As a result, introduced resistance fails because of increased Striga virulence (infection severity). This article reviews technologies for a new paradigm in Striga resistance breeding that incorporates host resistance breeding with well-informed knowledge of parasite resistance in order to ensure durability of resistance.

scholarly journals Modern Breeding Approaches for durable Resistance against the parasitic Plant Striga

Afrika Focus ◽  
2019 ◽  
Vol 32 (2) ◽  
Author(s):  
Steven Runo
Keyword(s):  
Host Resistance ◽  
Smallholder Farmers ◽  
Durable Resistance ◽  
Resistance Breeding ◽  
New Paradigm ◽  
Genome Wide ◽  
Striga Resistance ◽  
Severe Retardation ◽  
Modern Breeding ◽  
Great Danger

Crop losses caused by parasitic plants of the genus Striga pose a great danger to the livelihoods of millions of smallholder farmers in Africa. The parasite attaches to host crops and siphons nutrients leading to severe retardation and crop death. Controlling Striga is difficult because of the parasite’s ability to produce large amounts of seeds that can remain dormant in the soil for decades – only germinating in response to chemical cues (strigolactones) from the host. In recent years, breeding crops for host-based resistance has been prioritized. However, such programs have not taken into account Striga’s ability to overcome host resistance. As a result, introduced resistance fails because of increased Striga virulence (infection severity). This article reviews technologies for a new paradigm in Striga resistance breeding that incorporates host resistance breeding with well-informed knowledge of parasite resistance in order to ensure durability of resistance. KEY WORDS: STRIGA, HOST BASED RESISTANCE, GENOME WIDE ASSOCIATION MAPPING, RNA SEQUENCING

scholarly journals Race structure of cowpea witchweed (Striga gesnerioides) in West Africa and its implications for Striga resistance breeding of cowpea

Weed Science ◽  
2020 ◽  
Vol 68 (2) ◽  
pp. 125-133 ◽  
Author(s):  
Erik W. Ohlson ◽  
Michael P. Timko
Keyword(s):  
West Africa ◽  
Resistance Genes ◽  
Broad Spectrum ◽  
Genetic Relatedness ◽  
Durable Resistance ◽  
Resistance Breeding ◽  
Differential Resistance ◽  
African Countries ◽  
Sources Of Resistance ◽  
Striga Gesnerioides

AbstractCowpea witchweed [Striga gesnerioides (Willd.) Vatke] is a primary constraint of cowpea [Vigna unguiculata (L.) Walp.] production in West Africa. Previously, seven S. gesnerioides races were classified based upon host specificity and genotypic profiling. Because race number and distribution are dynamic systems influenced by gene flow, genetic drift, and natural selection, a thorough investigation of S. gesnerioides diversity and the effectiveness of known sources of resistance in cowpea is needed to develop varieties with durable and broad-spectrum Striga resistance. In this study, we screened seven cowpea lines against 58 unique S. gesnerioides populations collected from across nine West African countries. Individuals from 10 S. gesnerioides populations were genotyped with simple sequence repeat (SSR) markers. We identified six races of S. gesnerioides based on their parasitism of the seven cowpea lines with known differential resistance genotypes. No cowpea line was resistant to all 58 Striga populations and none of the Striga populations were able to overcome the resistance of all seven lines. A novel race, SG6, of the parasite collected from Kudu, Nigeria, was found to overcome more cowpea resistance genes than any previously reported race. SSR analysis indicates that Striga populations are highly differentiated and genetic relatedness generally corresponds with geographic proximity rather than their host compatibility. Due to the dearth of broad-spectrum resistance found among Striga-resistant cowpea lines, there exists a need to stack multiple Striga resistance genes in order to confer broad-spectrum and durable resistance.

scholarly journals A Comprehensive Review of the Major Genes Conditioning Resistance to Anthracnose in Common Bean

HortScience ◽  
2004 ◽  
Vol 39 (6) ◽  
pp. 1196-1207 ◽  
Author(s):  
James D. Kelly ◽  
Veronica A. Vallejo
Keyword(s):  
Common Bean ◽  
Resistance Genes ◽  
Durable Resistance ◽  
Gene Pyramiding ◽  
Resistance Breeding ◽  
Gene Clusters ◽  
Allelic Series ◽  
Multiple Alleles ◽  
Differential Cultivars ◽  
Major Resistance Genes

Resistance to anthracnose in common bean is conditioned primarily by nine major independent genes, Co-1 to Co-10 as the Co-3/Co-9 genes are allelic. With the exception of the recessive co-8 gene, all other nine are dominant genes and multiple alleles exist at the Co-1, Co-3 and Co-4 loci. A reverse of dominance at the Co-1 locus suggests that an order of dominance exists among individual alleles at this locus. The nine resistance genes Co-2 to Co-10 are Middle American in origin and Co-1 is the only locus from the Andean gene pool. Seven resistance loci have been mapped to the integrated bean linkage map and Co-1 resides on linkage group B1; Co-2 on B11, Co-3 on B4; Co-4 on B8; Co-6 on B7; and Co-9 and Co-10 are located on B4 but do not appear to be linked. Three Co-genes map to linkage groups B1, B4 and B11 where clusters with genes for rust resistance are located. In addition, there is co-localization with major resistance genes and QTL that condition partial resistance to anthracnose. Other QTL for resistance may provide putative map locations for the major resistance loci still to be mapped. Molecular markers linked to the majority of major Co-genes have been reported and these provide the opportunity to enhance disease resistance through marker-assisted selection and gene pyramiding. The 10 Co-genes are represented in the anthracnose differential cultivars, but are present as part of a multi-allelic series or in combination with other Co-genes, making the characterization of more complex races difficult. Although the Co-genes behave as major Mendelian factors, they most likely exist as resistance gene clusters as has been demonstrated on the molecular level at the Co-2 locus. Since the genes differ in their effectiveness in controlling the highly variable races of the anthracnose pathogen, the authors discuss the value of individual genes and alleles in resistance breeding and suggest the most effective gene pyramids to ensure long-term durable resistance to anthracnose in common bean.

scholarly journals Screening of sweetpotato germplasm collections for sweetpotato weevil (Cylas spp.) resistance in Tanzania

2020 ◽  
pp. 1707-1714
Author(s):  
Filson Kagimbo ◽  
Hussein Shimelis ◽  
Julia Sibiya
Keyword(s):  
Durable Resistance ◽  
Resistance Breeding ◽  
Root Weight ◽  
Root Number ◽  
Storage Roots ◽  
Damage Score ◽  
Sweetpotato Weevil ◽  
Lattice Design ◽  
Germplasm Collections ◽  
Western Tanzania

Weevil damage caused by sweetpotato weevil (Cylas spp.) is a major constraint to sweetpotato production in Tanzania due to a lack of improved varieties with durable resistance. The objective of this study was to screen sweetpotato germplasm collections for weevil resistance and to select the best parents to be used in resistance breeding. Field studies involving 96 sweetpotato genotypes were conducted at two weevil hotspot sites in Western Tanzania using a 12 x 8 lattice design with three replications at each site. Data collected included yield and yield related traits, weevil reaction and weevil damage score. The tested genotypes differed significantly (P < 0.01) for sweetpotato storage root number, root weight, root infestation and root damage score. Weevil infestation on storage roots significantly (P ≤0.05) correlated with total root number (r = 0.38) and weevil damage score (r = 0.79). Marketable root weight and total root weight were significantly correlated with infested root weight each with r = 0.45. The study identified nine sweetpotato genotypes expressing resistance and 10 genotypes with moderate resistance to weevil. Five genotypes including Magunhwa, Chuchu ya Nesi, Rugomoka, Tumauma and New Kawogo were selected with weevil resistance and desirable yield and yield-related traits. These genotypes can be used in future weevil resistance breeding programs of sweetpotato in Western Tanzania or related agro-ecologies.

scholarly journals Identification of candidate virulence loci in Striga hermonthica, a devastating parasite of African cereal crops

2022 ◽  
Author(s):  
Suo Qiu ◽  
James M. Bradley ◽  
Peijun Zhang ◽  
Roy Chaudhuri ◽  
Mark Blaxter ◽  
...  
Keyword(s):  
Host Resistance ◽  
Allelic Variation ◽  
Balancing Selection ◽  
Durable Resistance ◽  
Parasitic Plant ◽  
Sub Saharan Africa ◽  
Striga Hermonthica ◽  
Cell Wall Modification ◽  
A Genome ◽  
Wide Range

Parasites have evolved suites of proteins, Virulence Factors (VFs), that are delivered into host plants to facilitate colonization. Whilst VFs mediating plant-microbe and plant-nematode interactions have been characterised extensively, less is known about VFs mediating parasitic plant interactions with their hosts. Striga hermonthica is an obligate, root-parasitic plant capable of parasitizing multiple cereal hosts in sub-Saharan Africa, causing devastating losses in yields. An understanding of the molecular nature and allelic variation of VFs in S. hermonthica is essential for breeding durable resistance and delaying the evolution of parasite virulence. To address this issue, we assembled a genome for Striga hermonthica and identified candidate VFs by combining in silico prediction of secreted proteins with pooled sequencing of parasites growing on a susceptible and a strongly resistant rice host. Consistent with predictions for parasites, like S. hermonthica, that can interact with multiple hosts, we identified multiple loci, potentially with a wide range of functions, implicated in overcoming host resistance. Extremely different allele frequencies were observed at 152 non-secreted and 38 putatively secreted VFs between S. hermonthica parasitising the resistant and susceptible rice varieties. Our candidate, secreted VFs encompassed functions such as host cell wall modification, protease inhibitors, oxidoreductase and kinase activities, as well as several with unknown functions. Consistent with maintenance of variation at virulence loci by balancing selection the candidate loci had significantly higher Tajima’s D on average than the genomic background. Our results show that diverse strategies are used by  S. hermonthica  to overcome different layers of host resistance. Understanding the maintenance of variation at virulence loci by balancing selection will be critical to managing the evolution of virulence as a part of a sustainable control strategy.

scholarly journals Benefits of maize resistance breeding and chemical control against northern leaf blight in smallholder farms in South Africa

2020 ◽  
Vol 116 (11/12) ◽  
Author(s):  
Dave K. Berger ◽  
Tumisang Mokgobu ◽  
Katrien de Ridder ◽  
Nanette Christie ◽  
Theresa A.S. Aveling
Keyword(s):  
South Africa ◽  
Disease Resistance ◽  
Leaf Spot ◽  
Smallholder Farmers ◽  
Resistance Breeding ◽  
Leaf Blight ◽  
Northern Leaf Blight ◽  
Maize Hybrids ◽  
Kwazulu Natal ◽  
Disease Resistance Breeding

Maize underpins food security in South Africa. An annual production of more than 10 million tons is a combination of the output of large-scale commercial farms plus an estimated 250 000 ha cultivated by smallholder farmers. Maize leaves are a rich source of nutrients for fungal pathogens. Farmers must limit leaf blighting by fungi to prevent sugars captured by photosynthesis being ‘stolen’ instead of filling the grain. This study aimed to fill the knowledge gap on the prevalence and impact of fungal foliar diseases in local smallholder maize fields. A survey with 1124 plant observations from diverse maize hybrids was conducted over three seasons from 2015 to 2017 in five farming communities in KwaZulu-Natal Province (Hlanganani, Ntabamhlophe, KwaNxamalala) and Eastern Cape Province (Bizana, Tabankulu). Northern leaf blight (NLB), common rust, Phaeosphaeria leaf spot, and grey leaf spot had overall disease incidences of 75%, 77%, 68% and 56%, respectively, indicating high disease pressure in smallholder farming environments. NLB had the highest disease severity (LSD test, p<0.05). A yield trial focused on NLB in KwaZulu-Natal showed that this disease reduced yields in the three most susceptible maize hybrids by 36%, 71% and 72%, respectively. Eighteen other hybrids in this trial did not show significant yield reductions due to NLB, which illustrates the progress made by local maize breeders in disease resistance breeding. This work highlights the risk to smallholder farmers of planting disease-susceptible varieties, and makes recommendations on how to exploit the advances of hybrid maize disease resistance breeding to develop farmer-preferred varieties for smallholder production.

scholarly journals Marker-assisted pyramiding of two major broad-spectrum bacterial blight resistance genes,Xa21andXa33into an elite maintainer line of rice, DRR17B

2018 ◽  
Author(s):  
CH Balachiranjeevi ◽  
S Bhaskar Naik ◽  
V Abhilash Kumar ◽  
G Harika ◽  
H.K Mahadev Swamy ◽  
...  
Keyword(s):  
Resistance Genes ◽  
Bacterial Blight ◽  
Durable Resistance ◽  
Gene Pyramiding ◽  
Resistance Breeding ◽  
Fertility Restorer ◽  
Rice Varieties ◽  
Homozygous Condition ◽  
Specific Pcr ◽  
High Level

AbstractBacterial blight (BB) disease reduces the yield of rice varieties and hybrids considerably in many tropical rice growing countries like India. The present study highlights the development of durable BB resistance into the background of an elite maintainer of rice, DRR17B, by incorporating two major dominant genes,Xa21andXa33through marker-assisted backcross breeding (MABB). Through two sets of backcrosses, the two BB resistance genes were transferred separately to DRR17B. In this process, at each stage of backcrossing, foreground selection was carried out for the target resistance genes and for non-fertility restorer alleles concerning the major fertility restorer genesRf3andRf4, using gene-specific PCR-based markers, while background selection was done using a set of 61 and 64 parental polymorphic SSR markers respectively. Backcross derived lines possessing eitherXa21orXa33along with maximum genome recovery of DRR17B were identified at BC3F1generation and selfed to develop BC3F2s. Plants harboringXa21orXa33in homozygous condition were identified among BC3F2s and were intercrossed with each other to combine both the genes. The intercross F1plants (ICF1) were selfed and the intercross F2(ICF2) plants possessing bothXa21andXa33in homozygous condition were identified with the help of markers. They were then advanced further by selfing until ICF4generation. Selected ICF4lines were evaluated for their resistance against BB with eight virulent isolates and for key agro-morphological traits. Six promising two-gene pyramiding lines of DRR17B with high level of BB resistance and agro-morphological attributes similar or superior to DRR17B with complete maintenance ability have been identified. These lines with elevated level of durable resistance may be handy tool for BB resistance breeding.

Identification of Barley Lines with Resistance to Powdery Mildew Based on Seedling and Adult Plant Responses

2020 ◽  
Vol 55 (1) ◽  
pp. 3-10
Author(s):  
M. I. E. Arabi ◽  
M. Jawhar ◽  
E. Al-Shehadah
Keyword(s):  
Powdery Mildew ◽  
Powdery Mildew Resistance ◽  
Durable Resistance ◽  
Rapid Change ◽  
Resistance Breeding ◽  
Adult Plant ◽  
Growth Stages ◽  
Plant Responses ◽  
Genetic Stocks ◽  
Barley Germplasm

Powdery mildew (Blumeria graminis) is a major fungal disease of barley causing economical yield losses worldwide. Breeding for resistance to this disease is crucial due to the rapid change in pathotype patterns of B. graminis in fields. In the present work, powdery mildew-resistant barley germplasm was developed by crossing four cultivars currently used in Europe and West Asia. Out of 265 doubled haploid lines derived from these crosses, 40 lines were evaluated at seedling and adult stages. Data showed significant differences among barley lines with a continuum of resistance levels ranging from highly susceptible to tolerant which were consistent during the two growth stages. Two promising lines were more tolerant to powdery disease than the others. Across lines, there was a high correlation between field and greenhouse reaction (r=0.80, P<0.01), indicating the utility of greenhouse evaluations for screening barley for powdery mildew. This study suggests that, the newly identified resistance lines can serve as potential donors for ongoing powdery mildew resistance breeding program, and both types of seedling and adult plant resistance identified here can offer promising genetic stocks for accumulating both resistances to acquire durable resistance and long lasting control against B. graminis in Mediterranean and similar environments.

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