As the result of intensive research and breeding efforts over the last 20 years, the yield potential and yield quality of cereals have been greatly improved. Nowadays, yield safety has gained more importance because of the forecasted climatic changes. Drought and high temperature are especially considered as key stress factors with high potential impact on crop yield. Yield safety can only be improved if future breeding attempts will be based on the valuable new knowledge acquired on the processes determining plant development and its responses to stress. Plant stress responses are very complex. Interactions between plant structure, function and the environment need to be investigated at various phases of plant development at the organismal, cellular as well as molecular levels in order to obtain a full picture. The results achieved so far in this field indicate that various plant organs, in a definite hierarchy and in interaction with each other, are involved in determining crop yield under stress. Here we attempt to summarize the currently available information on cereal reproduction under drought and heat stress and to give an outlook towards potential strategies to improve yield safety in cereals.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2007.01727.x

The effect of drought and heat stress on reproductive processes in cereals.

▪ Abstract Domesticated plant taxa cannot be regarded as evolutionarily discrete from their wild relatives. Most domesticated plant taxa mate with wild relatives somewhere in the world, and gene flow from crop taxa may have a substantial impact on the evolution of wild populations. In a literature review of the world's 13 most important food crops, we show that 12 of these crops hybridize with wild relatives in some part of their agricultural distribution. We use population genetic theory to predict the evolutionary consequences of gene flow from crops to wild plants and discuss two applied consequences of crop-to-wild gene flow–the evolution of aggressive weeds and the extinction of rare species. We suggest ways of assessing the likelihood of hybridization, introgression, and the potential for undesirable gene flow from crops into weeds or rare species.

Gene Flow and Introgression from Domesticated Plants into Their Wild Relatives

Agriculture and climate change are internally correlated with each other in various aspects, as climate change is the main cause of biotic and abiotic stresses, which have adverse effects on the agriculture of a region. The land and its agriculture are being affected by climate changes in different ways, e.g., variations in annual rainfall, average temperature, heat waves, modifications in weeds, pests or microbes, global change of atmospheric CO2 or ozone level, and fluctuations in sea level. The threat of varying global climate has greatly driven the attention of scientists, as these variations are imparting negative impact on global crop production and compromising food security worldwide. According to some predicted reports, agriculture is considered the most endangered activity adversely affected by climate changes. To date, food security and ecosystem resilience are the most concerning subjects worldwide. Climate-smart agriculture is the only way to lower the negative impact of climate variations on crop adaptation, before it might affect global crop production drastically. In this review paper, we summarize the causes of climate change, stresses produced due to climate change, impacts on crops, modern breeding technologies, and biotechnological strategies to cope with climate change, in order to develop climate resilient crops. Revolutions in genetic engineering techniques can also aid in overcoming food security issues against extreme environmental conditions, by producing transgenic plants.

Impact of Climate Change on Crops Adaptation and Strategies to Tackle Its Outcome: A Review.

Reproductive development of plants is highly vulnerable to water deficit. Stress early during this phase can delay or completely inhibit flowering, both through an inhibition of floral induction and development. The stage of meiosis is perhaps the most stress-sensitive period of reproduction in all species studied. A meiotic-stage water deficit causes pollen sterility, but usually affects female fertility only under extreme stress. Sterility occurs even though the reproductive structures of stressed plants maintain a high water status, indicating that the response is probably mediated by a sporocidal signal from elsewhere in the plant. Rice and maize plants are also highly vulnerable during flowering (anthesis) and early grain initiation. Stress during this period can cause loss of pollen fertility, failure of pollination, spikelet death, or zygotic abortion. Changes in carbohydrate availability and metabolism appear to be involved in the effects of stress during meiosis and anthesis. Stress during early grain development curtails the kernel sink potential by reducing the number of endosperm cells and amyloplasts formed. Controls underlying these effects are poorly understood, although hormones may be involved. A water deficit during any stage of grain development causes the premature cessation of grain filling. Kernel moisture content and its direct impact on metabolism appear to be key regulatory factors in shortening the duration of grain filling.

Reproductive Development in Grain Crops during Drought

Water is the key resource limiting world agricultural production. Although an impressive number of research reports have been published on plant drought tolerance enhancement via genetic modifications during the last few years, progress has been slower than expected. We suggest a feasible alternative strategy by application of rhizospheric bacteria coevolved with plant roots in harsh environments over millions of years, and harboring adaptive traits improving plant fitness under biotic and abiotic stresses. We show the effect of bacterial priming on wheat drought stress tolerance enhancement, resulting in up to 78% greater plant biomass and five-fold higher survivorship under severe drought. We monitored emissions of seven stress-related volatiles from bacterially-primed drought-stressed wheat seedlings, and demonstrated that three of these volatiles are likely promising candidates for a rapid non-invasive technique to assess crop drought stress and its mitigation in early phases of stress development. We conclude that gauging stress by elicited volatiles provides an effectual platform for rapid screening of potent bacterial strains and that priming with isolates of rhizospheric bacteria from harsh environments is a promising, novel way to improve plant water use efficiency. These new advancements importantly contribute towards solving food security issues in changing climates.

/pdf/drought-tolerance-of-wheat-improved-by-rhizosphere-bacteria-4il6a1hpui.pdf

Drought-tolerance of wheat improved by rhizosphere bacteria from harsh environments: enhanced biomass production and reduced emissions of stress volatiles.

Several studies conducted under high input conditions have indicated little susceptibility of pearl millet to water deficit untill early grain filling, because the losses in main shoot production were fully compensated by increased tiller fertility. The present study assessed the impact of water deficits at three development stages: prior to flowering (S30), at the beginning of flowering (S45), and at the end of flowering (S60) in pearl millet grown in experimental conditions similar to Sahelian farming conditions. It included a control irrigation treatment simulating the natural distribution of rainfall throughout the cropping season. Both biomass production and grain yield were severely reduced by S30 and S45, while S60 had no effect. In S30 and S45, the flowering of tillers was delayed or totally inhibited. In both of these treatments, the low number of productive tillers did not compensate for damage to panicle initiation and flowering of the main shoot. All treatments maintained green leaves on the main shoot during the grain filling period, and in S30 leaf growth recovered from mid-season drought. These results illustrate how pearl millet mostly escapes drought by matching its phenology to the mean rainfall distribution in the Sahel. In the case of mid-season drought, some late productive tillers and the maintenance of green leaf biomass of the main shoots limited, but did not overcome, the yield losses. This study stresses the importance of agro-ecological conditions in control treatments, particularly the water regime and crop density, when assessing crop drought resistance.

Effect of the timing of water deficit on growth, phenology and yield of pearl millet (Pennisetum glaucum (L.) R. Br.) grown in Sahelian conditions

• Experiments are presented that test the relative importance, during ontogeny, of stomatal control and leaf area expansion to optimum seasonal water use in pearl millet (Pennisetum glaucum). These parameters play a key role in the compromise between plant growth and water saving under unpredictable conditions of semiarid environments.



• The response of growth and water use of crops to successive 15 d drought periods was measured under field conditions in Niger (West Africa).



• From emergence to anthesis, biomass partitioning to stems and panicles depended strongly on leaf area development. Water use was linearly related to green leaf area duration in well watered plots, but was reduced proportionally more than green leaf area in drought-affected plots. The relations of crop growth rate and transpiration efficiency to leaf area depended on ontogenetic changes in biomass partitioning.



• In P. glaucum, stomata play a dominant role in reducing crop water use under preanthesis drought, although this control becomes negligible after anthesis because of ontogenetic decline in the range of stomatal conductance. The rate of leaf senescence after anthesis is not drought-dependent.

https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers12-12/010038622.pdf

Ontogeny modifies the effects of water stress on stomatal control, leaf area duration and biomass partitioning of Pennisetum glaucum

In the Sahel region of Africa, the wild and the cultivated forms of pearl millet, Pennisetum glaucum (L.) R.Br., are sympatric and interfertile and yet have remained distinct for millenia. Reproductive barriers are not sufficient to explain this situation. To elucidate other possible mechanisms, the two forms were compared under experimental conditions in the Sahel for their phenology and reproductive effort. The length of the flowering period of each type was much longer than the average individual flowering period. When the last cultivated plants were finishing flowering, 65% of the wild plants were still flowering and 30% were just starting to flower. Thus, the last group was completely isolated from cultivated pearl millet gene flow (endogamic reproduction). The two forms of pearl millet also differed in the distribution of aboveground biomass among different plant parts, except for the number of seeds per plant. Both phenological behaviour and reproductive effort contribute to the maintenance of dist...

/pdf/phenology-and-reproductive-effort-of-cultivated-and-wild-173lbqzgvu.pdf

Phenology and reproductive effort of cultivated and wild forms of Pennisetum glaucum under experimental conditions in the Sahel : implications for the maintenance of polymorphism in the species

Under natural conditions, wild and cultivated pearl millet, Pennisetum glaucum (L.) R.Br., exchanged genes for millenia and, nevertheless, maintain high morphological differentiation. Under experim...

/pdf/experimental-study-of-gene-flow-between-wild-and-cultivated-sn11keywf6.pdf

Jean-François Renno

Papers

Effect of the timing of water deficit on growth, phenology and yield of pearl millet (Pennisetum glaucum (L.) R. Br.) grown in Sahelian conditions

Ontogeny modifies the effects of water stress on stomatal control, leaf area duration and biomass partitioning of Pennisetum glaucum

Phenology and reproductive effort of cultivated and wild forms of Pennisetum glaucum under experimental conditions in the Sahel : implications for the maintenance of polymorphism in the species

Experimental study of gene flow between wild and cultivated Pennisetum glaucum

Influence des pratiques culturales sur l'évolution de la fréquence des hybrides chibra dans un champ de mil, Pennisetum glaucum (L.) R. Br., au Sahel