This study was undertaken to determine phenotypic and genetic correlation coefficients among several agronomic traits in sugarcane (Saccharum spp.) and to analyze their interrelationships through path‐coefficient analyses. Other objectives were to determine broad‐sense heritability and genetic advance under selection for the traits studied. Random selections from two biparental crosses (‘CP 59‐50’ ✕ ‘CP 57‐603’ and ‘CP 62‐374’ ✕ ‘CP 57‐614’) were evaluated in the field for several attributes in plant cane, and first‐ and second‐ratoon crops. Genetic path‐coefficient analyses indicated plant height to be less important than stalk diameter and stalk number as a component of cane yield; but at the phenotypic level, all three components were of equal importance. Sucrose (%) had a large direct positive effect on sugar per ton of cane (S/T) whereas Brix (percent soluble solids) had a small negative direct influence on S/T. The S/T component exerted a greater direct effect on tons per hectare of sugar (THS) than did tons per hectare of cane (THC). Broad‐sense heritability estimates based plot means for various traits ranged from a low of 77% for THS to a high of 94% for stalk diameter. Expected genetic advance for various traits was reasonably high under selection intensities of 2 to 30%. THC estimated from the weight of a 10‐stalk sample per plot was genetically and phenotypically correlated with THC determined by weighing the entire plot (rg = 0.92, rp = 0.64) which suggested that a 10‐stalk sample per plot would be adequate to determine THC.

The central problem with any of the approaches for fine mapping is the limited number of meioses that have occurred and (in the case of advanced intercross lines) the cost of propagating lines to allow for a sufficient number of meioses. An alternative approach is 'association mapping', taking advantage of events that created association in the relatively distant past. Assuming many generations, and therefore meioses, have elapsed since these events, recombination will have removed association between a QTL and any marker not tightly linked to it. Association mapping thus allows for much finer mapping than standard biparental cross approaches. In this chapter review, association is first defined quantitatively and the mechanisms that generate it are described. To motivate the discussion of rigorous methods to test for marker association with a quantitative trait allele, a detailed discussion is provided for an example from the plant breeding literature. An analysis frequently used in human genetics to find marker associations with disease susceptibility alleles, the transmission/disequilibrium test (TDT), is reviewed. A brief discussion to extend the TDT to quantitative traits and to identify QTL × environment interactions is provided. The recent developments making use of multiple-marker haplotypes to locate QTL and some points concerning the power of association mapping are also discussed.

In a clonally propagated crop, such as potato (Solanum tuberosum L.), an estimate of genetic variance as a proportion of the total phenotypic variance (broad-sense heritability) is desirable. Because of its importance to the processing industry, tuber specific gravity has been widely studied. Earlier estimates of narrow-sense heritability for specific gravity in a diploid hybrid population of Solanum phureja × Solanum stenotomum (PHU-STN) were moderate. The purpose of this study was to identify stable, high specific gravity clones for future population improvement efforts and to estimate broad-sense heritability based on cloual means in this PHU-STN population. From 1990 to 1992, 72 diploid hybrid PHU-STN clones were grown in replicated field plots in Presque Isle, ME, and evaluated for specific gravity. There were significant differences among clones. There was also a significant replication (year) effect and clone × year interaction. From the analysis of variance on specific gravity, broad-sense heritability based on clonal means was estimated as 0.66, with a 95% confidence interval of 0.50 to 0.78. Stability-variance statistics calculated for each clone were used to identify stable high specific gravity clones. There was no correlation between average specific gravity during 3 yr and the stability-variance statistic, indicating that selecting for high specific gravity should not result in clones that are less stable for specific

Seeds contaminated with pathogens are the primary inoculum for plant diseases in many food crops. Conventional treatments for seedborne diseases use hot water, chlorine or fungicide applications. A novel seed treatment method based on non‐thermal plasma generated by an air dielectric barrier discharge (DBD) device was evaluated in this study as an alternative to these conventional treatments. The non‐thermal plasma at atmospheric pressure and room temperature consisted of partially‐ionized gases that are chemically reactive. The antimicrobial activity of non‐thermal plasma was evaluated against an important seedborne pathogen, Gibberella fujikuroi, that causes bakanae disease in rice. Non‐thermal plasma treatments effectively inhibited the growth of G. fujikuroi on nutrient growth medium and reduced the number of fungal colony forming units (CFU) on the rice seed surface by > 92% after 120 s exposure. Effective exposure times to 50% (ET50) and 90% (ET90) control of G. fujikuroi CFU on the seed surface were 9 and 76 s, respectively. Ten minutes of non‐thermal plasma treatment on seeds infested with G. fujikuroi significantly reduced disease development. No adverse effects were detected on the seedling emergence and height when non‐infested seeds were treated with non‐thermal plasma for up to 20 min. The treated seeds germinated and grew similarly compared with non‐treated non‐infested seeds. This study indicates that non‐thermal plasma had antifungal activity and showed potential as an effective disinfection technique to reduce the contamination of seedborne fungal pathogens from seed surfaces without compromising seed health.

This chapter focuses on the importance of genotype environment interactions in plant and animal breeding. The role of plant breeders in identifying genes or QTLs conditioning resistance/tolerance to biotic and abiotic stresses is discussed and the role of molecular biology (including molecular genetics, biochemistry and plant physiology)in breeding crop species and overcoming the constraints imposed on genotypes by their interaction with environmental factors are also pointed out.