KASPar SNP genetic map of cassava for QTL discovery of productivity traits in moderate drought stress environment in Africa

Open Access Journal; Published online: 28 May 2021Cassava is an important staple in Sub-Sahara Africa. While its production has rapidly expanded to the dry savannahs of the continent, productivity is low in this ecology due to drought by farmers, extending the growth cycle from 12 months to 18, and sometimes 24 months to ensure better harvests. Yield is a complex trait and often difficult to manipulate for genetic gain in conventional breeding. Unfortunately, the dearth of molecular tools for decades has hampered molecular breeding (MB) to improve cassava productivity. This study was conducted to explore KASpar SNPs to generate more molecular tools to enhance genetic dissection of elite African germplasm for improved cassava productivity in dry environments of Africa where molecular resources are highly limited for crop improvement. To aid molecular genetic analysis of traits, a linkage map covering 1582.8 cM with an average resolution of 3.69 cM was constructed using 505 polymorphic SNP markers distributed over 21 linkage groups. Composite interval mapping using 267 F1 progeny in initial QTL mapping identified 27 QTLs for productivity traits in the dry savannah of Nigeria. The availability of KASPar SNPs are anticipated to improve the implementation of MB for the development of high performing drought-tolerant cassava varieties in Africa

Evaluation Of Cassava Cultivars For Canopy Retention And Its Relationship With Field Resistance To Green Spider Mite

Three field trials were conducted at IITA, Ibadan, Nigeria between 1993 and 1995 to identify a rapid method of screening cassava (Manihot esculenta Crantz) cultivars for canopy retention and to determine the association between canopy retention and resistance to green spider mite (Mononychellus tanajoa Bondar) in cassava. Three methods (I, II and III) were used to assess canopy retention in 70 cultivars. Method I involves visual estimation and it takes the longest time; method II involves visual estimation and it takes the shortest time; and method III involves taking measurements and it takes a longer time than method II, but with a much shorter time than method I. Method II was the best method for screening cassava cultivars for canopy retention during dry periods. The cultivars showed significant (P < 0.01) differences for canopy retention, stay green ability, mite population density and damage scores, but not for relative water content. Canopy retention was positively correlated (P < 0.01) with stay green ability at the peak of the dry season (January). Generally, canopy retention and stay green ability were inversely associated (P < 0.01) with mite density in March 1994 and 1995, and with damage during the dry season (December to March 1994 and 1995, respectively). It is proposed that cassava cultivars which are tolerant to drought may also be resistant to M. tanajoa and that the genetic potential of cassava to retain many green leaves during the dry season may be a major factor of resistance to M. tanajoa.Trois essais en champs ont \ue9t\ue9 men\ue9s \ue0 l ' IITA \ue0 Ibadan au Nigeria entre 1993 et 1995 pour identifier une m\ue9thode rapide de criblage des cultivars de manioc (Manihot esculenta Crantz) pour la r\ue9tention foliaire et la capacit\ue9 de rester vert, et de d\ue9terminer la relation entre la r\ue9tention foliaire et la resistance \ue0 l ' acarien vert du manioc (Mononychellus tanajoa Bondar). Trois m\ue9thodes (I, II et III) ont \ue9t\ue9 utilis\ue9es pour \ue9valuer la r\ue9tention foliaire chez 70 cultivars. La m\ue9thode I implique l'estimation visuelle et elle prend le temps plus long; la m\ue9thod II implique l'estimation visuelle et elle prend le temps plus court; et la m\ue9thode III implique les mesures et elle prend un temps plus long que celui de la m\ue9thode II, mais beaucoup plus court que celui de la m\ue9thode I. La m\ue9thode II a \ue9t\ue9 la meilleure m\ue9thode de criblage des cultivars de manioc pour la r\ue9tention foliaire pendant les p\ue9riodes s\ue8ches. Il y avait des diff\ue9rences significatives (P < 0,01) entre les cultivars pour la r\ue9tention foliaire, la capacit\ue9 de rester vert, la densit\ue9 des acariens et des d\ue9g\ue2ts caus\ue9s par des acariens mais pas pour la teneur relative en eau. Des corr\ue9lations positives ont \ue9t\ue9 not\ue9es entre la r\ue9tention foliare et la capacit\ue9 de rester vert au pic de la saison seche (Janvier). En g\ue9n\ue9ral, la r\ue9tention foliaire et la capacit\ue9 de rester vert \ue9taient invers\ue9ment associ\ue9es (P < 0,01) \ue0 la densit\ue9 des acariens en Mars 1994 et 1995, et avec des d\ue9g\ue2ts caus\ue9s par l'acarien pendant la saison s\ue8che (de D\ue9cembre \ue0 Mars 1994 et 1995). Il ressort de ces r\ue9sultats que les cultivars de manioc qui sont tol\ue9rants \ue0 la s\ue9cheresse semblent aussi r\ue9sistants \ue0 M. tanajoa et que le potentiel g\ue9n\ue9tique du manioc \ue0 retenir ses feuilles pendant la saison s\ue8che peut \ueatre un facteur majeur de r\ue9sistance au M. tanajoa

Evaluation of cassava cultivars for canopy retention and its relationship with field resistance to green spider mite

Three field trials were conducted at IITA, Ibadan, Nigeria between 1993 and 1995 to identify a rapid method of screening cassava (Manihot esculenta Crantz) cultivars for canopy retention and to determine the association between canopy retention and resistance to green spider mite (Mononychellus tanajoa Bondar) in cassava. Three methods (I, II and III) were used to assess canopy retention in 70 cultivars. Method I involves visual estimation and it takes the longest time; method II involves visual estimation and it takes the shortest time; and method III involves taking measurements and it takes a longer time than method II, but with a much shorter time than method I. Method II was the best method for screening cassava cultivars for canopy retention during dry periods. The cultivars showed significant (P < 0.01) differences for canopy retention, stay green ability, mite population density and damage scores, but not for relative water content. Canopy retention was positively correlated (P < 0.01) with stay green ability at the peak of the dry season (January). Generally, canopy retention and stay green ability were inversely associated (P < 0.01) with mite density in March 1994 and 1995, and with damage during the dry season (December to March 1994 and 1995, respectively). It is proposed that cassava cultivars which are tolerant to drought may also be resistant to M. tanajoa and that the genetic potential of cassava to retain many green leaves during the dry season may be a major factor of resistance to M. tanajoa