Herbicides targeting grass plastidic acetyl coenzyme A carboxylase (ACC) are effective selective graminicides. Their intensive use worldwide has selected for resistance genes in a number of grass weed species. Biochemistry and molecular biology have been the means of determining the herbicidal activity and selectivity toward crop plants of ACC-inhibiting herbicides. In recent years, elucidation of the tridimensional structure of ACC and identification of five amino acid residues within the ACC carboxyl transferase domain that are critical determinants for herbicide sensitivity shed light on the basis of ACC-based resistance to herbicides. However, metabolism-based resistance to ACC-inhibiting herbicides is much less well known, although this type of resistance seems to be widespread. A number of genes thus endow resistance to ACC-inhibiting herbicides, with the possibility for various resistance genes that confer dominant resistance at the herbicide field rate to accumulate within a single weed population or plant. This, together with a poor knowledge of the genetic parameters driving resistance, renders the evolution of resistance to ACC-inhibiting herbicides unpredictable. Future research should consider developing tactics to slow the spread of resistance. For this purpose, it is crucial that our understanding of metabolism-based resistance improves rapidly because this mechanism is complex and can confer resistance to herbicides with different target sites.

Production of summer squash, Cucurbita pepo, can be severely limited by viral pathogens and powdery mildew. Resistance has been introgressed from Cucurbita moschata, and resistant hybrids have been commercially deployed. Our objective was to assess genetic affinities of such hybrids with susceptible, open-pollinated cocozelle and zucchini cultivars, and two disease-resistant lines derived from six generations of backcrossing to a susceptible zucchini cultivar. Amplified fragment length polymorphism (AFLP) EcoRI/MseI primer combinations were employed and, based on the resulting polymorphic bands, genetic similarities were estimated, and an unweighted pair group method using arithmetic average (UPGMA) cluster analysis was conducted. The open-pollinated cocozelle cultivars clustered with the resistant hybrids. The hybrids had greater similarities with one another than did the open-pollinated cultivars. The zucchini cultivars and their resistant backcross lines formed their own exclusive cluster. However, the resistant backcross lines showed less than 0.80 similarity with their recurrent parent. As the chromosome number of Cucurbita is high (2n = 2x = 40) and the resistances are inherited monogenically and oligogenically, these results, after six generations of backcrossing, cannot be explained by classical genetic linkage.

Chickpea (Cicer arietinum L.) is an important crop for developed as well as underdeveloped countries, especially those in the Indian sub-continent that contribute more than 60% to both the global area and global production. The harsh environmental conditions under which chickpeas are generally grown impose restrictions on the expression of genetic yield potential. In the present study, a number of different breeding approaches for the development of genotypes possessing multiple resistances to different biotic and abiotic stresses, coupled with enhanced productivity are reported. In one study, 90 genetically diverse genotypes (35 medium-sized desi types, 35 bold-seeded desi types, 10 medium-sized kabuli types and 10 bold-seeded kabuli types) were tested in several locations in the 2000–2002 seasons, under rainfed (dryland) conditions and with supplemental irrigation. The bold-seeded desi genotypes gave superior performance in the rainfed environment, while the bold-seeded kabuli genotypes outyielded the other cultivars under supplemental irrigation. From crosses between accessions from geographically diverse sources, crosses between lines carrying multiple disease resistances, and crosses between the cultivated chickpea and the wild species, C. reticulatum, 23 selections were tested for yield and resistance to multiple stresses at various locations in northern and central India. From the crosses between geographically diverse parents, six high-yielding kabuli genotypes with wide adaptation and drought tolerance were identified. Pyramiding genes for multiple resistances proved useful in identifying eight lines possessing multiple disease resistance. Introgressing wild genes generated nine genotypes with high yield potential, resistance to soil-borne diseases and adaptation to water-limited environments. We conclude that high productivity, multiple resistance and wide adaptability can be achieved simultaneously by using potentially complementary approaches.