Understanding of terminal drought tolerance mechanisms in pearl millet (Pennisetum glaucum (L.) R. Br.)

The main objective of the thesis work was the detailed characterization of pearl millet (Pennisetum glaucum (L.) R. Br.) genotypes contrasting for terminal drought tolerance. For that work, we used a set of near isogenic lines (NIL-QTLs; carrying terminal drought tolerance quantitative trait locus (QTL) from a drougth tolerant donor parent on the genetic background of a sensitive parent) and a recombinant inbred lines population (RIL; developed from a cross between the tolerant and sensitive genotype). In these contrasting genotypes we investigated following physiological traits. Transpiration rate (Tr), transpiration efficiency (TE), transpiration response to increased vapor pressure deficit, threshold in volumetric soil moisture where transpiration begins to decline (FTSW threshold), stomatal density (SD), sensitivity of plants’ growth to VPD below and above 2kPa. Regarding biochemical traits, we followed content of chlorophyll (Chl), carotenoids (Car), abscisic acid (ABA), proline (Pro), we conducted isozyme analysis of antioxidative enzymes [superoxid dismutase (SOD), ascorbic peroxidase (APX), catalase (CAT)]. The main leading thread for understanding the drought tolerance mechanisms of pearl millet came from the analysis of traits related to the control of water losses under fully irrigated conditions. We could clearly distinguish drought tolerant genotypes from the sensitive ones based on: i) lower Tr in well-watered conditions measured on full plant basis and on detached leaves ii) higher leaf ABA content in well-watered conditons iii) sensitivity of transpiration to high VPD condition under well-watered conditions. Furthemore, the leaf expansion of tolerant genotypes was sensitive to VPD conditions in which plant development took place and these conditions determined the dynamics of water utilisation during plants development. Based on the biochemical parameters we could rarely distinquish between tolerant and sensitive genotype. Though we documented differences in the activity of APX5 isoenzyme and proline accumulation dynamics under water limiting conditions between tolerant/sensitive genotypes, this variation was probably not directly linked to the yield variation of these genotypes under terminal drought conditions. It is concluded that the major terminal drought tolerance mechanism of investigated tolerant pearl millet genotypes is linked to their lower Tr. Low Tr of these genotypes probably contribute to saving the water in the soil profile and so leaving a critical amount of water available for grain filling stage (in fact drought avoidance mechanism). It is further discussed that Tr could be influenced by the level of leaf ABA and the hydraulic properties of plant tissues. However, these “water saving” drought tolerance mechanisms seems to be specific to the environmental conditions in which plants` development took place. The importance of these water saving mechanisms is also being validated in RIL population. The biochemical parameters tested under drought conditions appeared to have no major significance for terminal drought tolerance

Constitutive water-conserving mechanisms are correlated with the terminal drought tolerance of pearl millet [Pennisetum glaucum (L.) R. Br.]

Pearl millet, a key staple crop of the semi-arid tropics, is mostly grown in water-limited conditions, and improving its performance depends on how genotypes manage limited water resources. This study investigates whether the control of water loss under non-limiting water conditions is involved in the terminal drought tolerance of pearl millet. Two pairs of tolerant×sensitive pearl millet genotypes, PRLT 2/89-33–H77/833-2 and 863B-P2–ICMB 841-P3, and near-isogenic lines (NILs), introgressed with a terminal drought tolerance quantitative trait locus (QTL) from the donor parent PRLT 2/89-33 into H77/833-2 (NILs-QTL), were tested. Upon exposure to water deficit, transpiration began to decline at lower fractions of transpirable soil water (FTSW) in tolerant than in sensitive genotypes, and NILs-QTL followed the pattern of the tolerant parents. The transpiration rate (Tr, in g water loss cm−2 d−1) under well-watered conditions was lower in tolerant than in sensitive parental genotypes, and the Tr of NILs-QTL followed the pattern of the tolerant parents. In addition, Tr measured in detached leaves (g water loss cm−2 h−1) from field-grown plants of the parental lines showed lower Tr values in tolerant parents. Defoliation led to an increase in Tr that was higher in sensitive than in tolerant genotypes. The differences in Tr between genotypes was not related to the stomatal density. These results demonstrate that constitutive traits controlling leaf water loss under well-watered conditions correlate with the terminal drought tolerance of pearl millet. Such traits may lead to more water being available for grain filling under terminal drought

Chickpea Genotypes Contrasting for Vigor and Canopy Conductance Also Differ in Their Dependence on Different Water Transport Pathways

Lower plant transpiration rate (TR) under high vapor pressure deficit (VPD) conditions and early plant vigor are proposed as major traits influencing the rate of crop water use and possibly the fitness of chickpea lines to specific terminal drought conditions—this being the major constraint limiting chickpea productivity. The physiological mechanisms underlying difference in TR under high VPD and vigor are still unresolved, and so is the link between vigor and TR. Lower TR is hypothesized to relate to hydraulic conductance differences. Experiments were conducted in both soil (Vertisol) and hydroponic culture. The assessment of the TR response to increasing VPD showed that high vigor genotypes had TR restriction under high VPD, and this was confirmed in the early vigor parent and progeny genotype (ICC 4958 and RIL 211) having lower TR than the late vigor parent and progeny genotype (ICC 1882 and RIL 022). Inhibition of water transport pathways [apoplast and symplast (aquaporins)] in intact plants led to a lower transpiration inhibition in the early vigor/low TR genotypes than in the late vigor/high TR genotypes. De-rooted shoot treatment with an aquaporin inhibitor led to a lower transpiration inhibition in the early vigor/low TR genotypes than in the late vigor/high TR genotypes. Early vigor genotypes had lower root hydraulic conductivity than late vigor/high TR genotypes. Under inhibited conditions (apoplast, symplast), root hydraulic conductivity was reduced more in the late vigor/high TR genotypes than in the early vigor/low TR genotypes. We interpret that early vigor/low TR genotypes have a lower involvement of aquaporins in water transport pathways and may also have a smaller apoplastic pathway than high TR genotypes, which could explain the transpiration restriction under high VPD and would be helpful to conserve soil water under high evaporative demand. These findings open an opportunity for breeding to tailor genotypes with different “dosage” of these traits toward adaptation to varying drought-prone environments

Machine Learning-Based Plant Detection Algorithms to Automate Counting Tasks Using 3D Canopy Scans

This study tested whether machine learning (ML) methods can effectively separate individual plants from complex 3D canopy laser scans as a prerequisite to analyzing particular plant features. For this, we scanned mung bean and chickpea crops with PlantEye (R) laser scanners. Firstly, we segmented the crop canopies from the background in 3D space using the Region Growing Segmentation algorithm. Then, Convolutional Neural Network (CNN) based ML algorithms were fine-tuned for plant counting. Application of the CNN-based (Convolutional Neural Network) processing architecture was possible only after we reduced the dimensionality of the data to 2D. This allowed for the identification of individual plants and their counting with an accuracy of 93.18% and 92.87% for mung bean and chickpea plants, respectively. These steps were connected to the phenotyping pipeline, which can now replace manual counting operations that are inefficient, costly, and error-prone. The use of CNN in this study was innovatively solved with dimensionality reduction, addition of height information as color, and consequent application of a 2D CNN-based approach. We found there to be a wide gap in the use of ML on 3D information. This gap will have to be addressed, especially for more complex plant feature extractions, which we intend to implement through further research. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Response of selected physiological and morphological parameters of maize to Hypoxia/Posthypoxia crowing conditions and their genetic determination

Department of Genetics and MicrobiologyKatedra genetiky a mikrobiologiePřírodovědecká fakultaFaculty of Scienc

Srovnání C3 a C4 plodin z hlediska tolerance k salinitnímu a vodnímu stresu

The main objective of the thesis work was the detailed characterization of pearl millet (Pennisetum glaucum (L.) R. Br.) genotypes contrasting for terminal drought tolerance. For that work, we used a set of near isogenic lines (NIL-QTLs; carrying terminal drought tolerance quantitative trait locus (QTL) from a drougth tolerant donor parent on the genetic background of a sensitive parent) and a recombinant inbred lines population (RIL; developed from a cross between the tolerant and sensitive genotype). In these contrasting genotypes we investigated following physiological traits. Transpiration rate (Tr), transpiration efficiency (TE), transpiration response to increased vapor pressure deficit, threshold in volumetric soil moisture where transpiration begins to decline (FTSW threshold), stomatal density (SD), sensitivity of plants' growth to VPD below and above 2kPa. Regarding biochemical traits, we followed content of chlorophyll (Chl), carotenoids (Car), abscisic acid (ABA), proline (Pro), we conducted isozyme analysis of antioxidative enzymes [superoxid dismutase (SOD), ascorbic peroxidase (APX), catalase (CAT)]. The main leading thread for understanding the drought tolerance mechanisms of pearl millet came from the analysis of traits related to the control of water losses under fully irrigated...SOUHRN Cílem této práce byla detailní studie genotypů prosa (Pennisetum glaucum (L.) R. Br.), které byly dříve testovány v polních podmínkách a shledány jako kontrastní v toleranci k pozdnímu stresu suchem (vzhledem k výnosům). Dále jsme se zaměřili na identifikaci klíčových znaků a mechanizmů, které významně ovlivňují toleranci k pozdnímu stresu suchem nejen na tomto kontrastním materiálu, ale i na "téměř isogenních liniích" (near isogenic lines; NIL-QTLs, což jsou linie nesoucí lokus kvantitativního znaku (quantitative trait locus; QTL) původem z tolerantního genotypu na genetickém pozadí citlivého genotypu) a na populaci rekombinantních imbredních liniích (recombinant imbred lines; RIL, což je populace linií vzniklá křížením toleraního a citlivého genotypu). Na kontrastních genotypech jsme měřili: Rychlost transpirace (Tr), transpirační výkon (TE), odezvu transpirace na změny v tenzi vodních par (vapor pressure deficit, VPD), hranici půdni vlhkosti, kdy dochází k omezení transpirace (FTSW threshold), počet stomat (SD), citlivost rostlinného růstu k VPD podmínkám. Z biochemických parametrů jsme stanovovali obsah chlorofylu (Chl), karotenoidů (Car), kyseliny abscisové (ABA), prolinu (Pro) a analyzovali jsme izoenzymové spektrum a aktivitu antioxidativních enzymů [superoxid dismutasa (SOD), askorbát...Department of Genetics and MicrobiologyKatedra genetiky a mikrobiologieFaculty of SciencePřírodovědecká fakult