Improved methodologies for breeding striga-resistant sorghums

TLDR: Agarwal et al. as discussed by the authors reviewed methodologies for breeding striga-resistant sorghums, including the use of agar-gel assay to screen host genotypes in the laboratory for low production of the striga seed germination stimulant.

About: This article is published in Field Crops Research.The article was published on 2000-06-01 and is currently open access. It has received 182 citations till now. The article focuses on the topics: Striga.

Figures

Table 2 Description of nine striga vigor classes

Fig. 1. Simpli®ed life cycle of striga (modi®ed from Ejeta et al., 1992).

Table 1 Summary of striga control methods in cerealsa

Fig. 2. Mean and individual estimates of the heritability in a replicated trial (%) across 50 sorghum entries for all possible permutations of two, three, four, ®ve, and the actually available six replications, for the number of emerged striga plants per m2 in ®eld trials at Samanko, Mali, 1996 (82 d.a.p.) and Alupe, Kenya, in the Short Rainy Season 1996/1997 (85 d.a.p.).

Frequently asked questions

Q1. What are the contributions in "Improved methodologies for breeding striga-resistant sorghums" ?

In this paper the authors review methodologies for breeding striga-resistant sorghums. An improved ®eld testing methodology should include one or several of the following practices: ®eld inoculation with striga seeds ; appropriate experimental design including elevated replication number ; speci®c plot layout ; use of appropriate susceptible and resistant checks ; evaluation in adjacent infested and uninfested plots ; and the use of selection indices derived from emerged striga counts, striga vigor, and grain yield or a host plant damage score. Further laboratory assays are needed which allow the non-destructive, rapid and inexpensive evaluation of individual plants for additional resistance mechanisms. This approach is particularly promising because striga resistance tests are dif®cult, expensive, and sometimes unreliable ; the parasite is quarantined ; and some resistance genes are recessive. 

Q2. What are some examples of region-speci®c selection traits?

Grain color and quality, plant height, maturity, photoperiod sensitivity, and disease resistance are examples for region-speci®c selection traits. 

Q3. What are the prerequisites for high cost effectiveness of herbicide treatments?

The great ef®cacy and low labor and energy requirements of herbicide treatments are important prerequisites for high cost effectiveness. 

Q4. How many replications are necessary for striga trials?

The authors conclude that a minimum of four replications is essential for striga trials to reduce the risk of experimental failure due to the natural heterogeneity within experimental areas. 

Q5. What is the role of striga in the survival of the plant?

Because striga is an obligate parasite, interactions between striga and its host plant play a crucial role in the survival of the parasite. 

Q6. What are the main prerequisites for an indirect selection trait?

With its high heritability and the possibility to screen large numbers of entries, the in vitro germination distance ful®lls two major prerequisites for an indirect selection trait. 

Q7. How many kilo of striga seed are used to infest an experimental area?

Three to four kilogram of clean, viable striga seed (with about 190 viable grains per mg) are suf®cient to heavily infest an experimental area of 1 ha. 

Q8. What is the main consideration of integrated striga control strategies?

Another consideration involving herbicide-tolerant crops as components of integrated striga control strategies is the ability of farmers to purchase improved seed and the herbicide. 

Q9. How many sorghum recombinant populations were evaluated in the study?

The geneticmaterials evaluated in these trials consisted of two sorghum recombinant inbred populations with 121 entries each, planted in 11 11 lattice designs with six replications at various locations in both East and West Africa. 

Q10. What is the need for national programs in Africa to screen legume cultivars?

There is a need for national programs in Africa to screen legume cultivars at the local level, to identify those that effectively stimulate germination of local striga strains. 

Q11. What is the potential merit of sorghum hybrids?

The potential merit of heterozygous sorghum cultivars was demonstrated by the average superiority of F2 populations over their parental lines of 18% for grain yield under striga infestation, averaged across four locations in Mali and Kenya (Haussmann et al., 2000a). 

Q12. What is the way to reduce the number of test locations?

If seed shortage imposes a constraint on progeny evaluation, a reduction in plot size should be preferred over reduction of the number of test locations, since there is always the danger of loosing data from one location due to `̀ non-striga years'' or other obstacles. 

Q13. What are the traits of striga that are frequently assessed?

The following striga traits are frequently assessed: days to striga emergence and days to onset of striga ¯owering in each plot; total number of emerged striga plants; number of ¯owering striga plants; and number of striga plants with seed capsules (i.e., to measure the reproductive success of striga). 

Q14. How many striga plants are attached to the roots?

Assessment of the number of subterranean attached striga plants, i.e., striga plants which are attached to the roots but have not emerged above ground, is very laborious and is only practical in small trials or with selected entries in a large trial.