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ABSTRACT. Weed incursion in cultivated fields is a serious biological problem, which causes considerable yield losses of economically important field crops through allelopathy and competitive interactions. Spotted knapweed (Centaurea maculosa) and yellow melilot (Melilotus officinalis) are among the most prevalent weeds in cultivated fields of Pakistan, particularly in wheat fields. Like many other weeds, they may pose allelopathic and competitive challenges to field crops. The objective of this study was to evaluate allelopathic potentials of the two weeds on germination and seedling growth of wheat under laboratory conditions. Amounts of 15, 20, 25 and 30% concentrated leaf aqueous extracts of C. maculosa and M. officinalis were prepared and tested for their effects on germination percentage, radicle and coleoptile lengths of wheat. Germination, radicle and coleoptile lengths of test crop declined significantly at higher concentration (25-30%) of the extracts of two weeds. However, concentration of M. officinalis up to 20% had either no effect or stimulatory effects on the studied growth characteristics of wheat. Highest germination inhibition and decreased seedling growth were caused by leaf extracts of C. maculosa at 30% extract concentration. Growth inhibition was generally dependent on the extract concentration. The study indicated that both plant exhibited allelopathic activity and growth inhibitory effects on wheat at higher concentration;however, extracts of C. maculosa were more phytoinhibitory

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Summary Late blight of potato and tomato, one of the most widely reported diseases of plants, is a significant curb in global agriculture which poses severe problems in terms of yield and economic losses, and environmental pollution due to pesticides use. The disease is caused by Phytophthora infestans -an oomycete - which first drew the considerable attention of plant pathologists during the mid-1840s when the pathogen incited historic starvation in Ireland – the great Irish potato famine - as a consequence of substantial potato losses due to late blight disease. Since that period, late blight has triggered several epidemics of potato and tomato of profound intensity in different regions. Over the course, synthetic fungicides have been proved effective management practice for late blight control; nonetheless, the evolution of new genotypes with increased virulence to hosts and resistance to fungicides has been greatly regarded as an agricultural problem. Breakthroughs in genome sequencing of P. infestans and identification of resistance genes in some plants have opened ways for the development of resistant genotypes. However, there still exist numerous challenges to deal with this noxious pathogen. This review aims to highlight the historical significance of late blight disease, its chemical control strategies and associated challenges, and resistance breeding programs by employing genetic approaches.