Phosphorus and micronutrient (Fe, Mn, Cu & Zn) behaviour was investigated under flooded and aerated soil conditions, typical of paddy rice and wheat rotations in Pakistan. Pyrophosphate was used in small proportions with orthophosphate to investigate its effects on P and micronutrient, particular Zn availability, during both laboratory incubations and glass house experiments. Hydrolysis of pyrophosphate, its effects on P sorption by lime and different soils with or without added "organic acids" were also studied. Flooded conditions during both laboratory incubations and glass house trials greatly increased the extractability of soil P in comparison to controls and orthophosphate treated samples. Moist aerated conditions enhanced the sorption of applied P, with further sorption being observed in alternating flooded and moist aerated conditions. Increases in the extractability of soil P were related to iron oxidases/hydroxides. Soil Fe, Mn and Cu increased with flooding whereas soil Zn decreased. Soil P availability increased with the addition of lime, the 10% level being more effective than 5%, either due to increases in pH and/or due to precipitation of iron, the active site for P sorption. Pyrophosphate with or without added Zn decreased p sorption by lime and the soils studied, with the greatest effects being observed in the presence of lime. Added pyrophosphate, in the presence of lime, also maintained lower pH values in the solution compared with orthophosphate treated samples. Among the soils, pyrophosphate proved to be more effective when added to a calcareous Pakistani soil rather than the local soils (brown earth + brown podzolic). Added "organic acids", like extracts of soil and rice straw, decreased P sorption whereas the addition of (0.1M) citric acid increased it. Added Zn decreased P sorption by agricultural lime and the soils studied. In the presence of added pyrophosphate, sorption of Zn by agricultural lime decreased whereas sorption increased in soils.

Crop domestication and subsequent breeding or directional selection have narrowed the genetic diversity of elite varieties whereas land races, ecotypes, wild relatives growing on native preferences still keep genetic diversities of stress tolerances. Rayada is such an exceptional ecotype, variant of typical deepwater rice, completely endemic to certain areas of Madhumati river tracts of Bangladesh and still shares some features of wild rices. Multiple physiological features of Rayadas are distinctly different from typical deepwater rice. In this PhD project, we have studied the specialty of Rayada rice and identified that Rayada has special tolerances to prolonged flood, submergence and cold along with longer root system and prompt recovery capacity after water stress. All these features make it as an elite resource of stress tolerance and might become a new focus of rice germplasm research. Among all deepwater rices, Rayada is the only exception, having virtually no seed dormancy, but both physiological and molecular bases of this trait are completely unknown. We examined the non-dormant nature of Rayadas as a natural variant of deepwater rice. After comparing features of freshly harvested seeds of Rayada with those of typical deepwater rice variety, we identified several concerted features; for instance, less ABA content in freshly harvested seeds; faster ABA catabolism and enhanced ROS accumulation after imbibition. Moreover, after analyzing stepwise gene expressions of 32 bZIPs in seed germination, mild and severe water stresses among three extreme ecotypes including Rayadas together with homology search with reported genes, we identified OsbZIP84 as a candidate gene for the regulation of ABA catabolism in Rayada rice. ABA content and expression analysis of OsbZIP84 and ABA8oxs in four growth and developmental stages along with phenotyping of mutant revealed the function of OSbZIP84 in the dormancy regulation of Rayada rice. Submergence tolerance during seed germination is one of the rare traits of rice, even among cereals. Except few physiological indications of tolerance, most other molecular signaling network is not known. We identified several positive and negative regulators of shoot development under submergence inducting the capacity of shoot development of Rayada rice under oxidative stress. We successfully developed a condition supplemented with riboflavin and H2O2 where intolerant genotypes successfully developed shoot under submergence. However, induced shoot development was completely inhibited by glucose, ABA and mitochondrial complex IV inhibitor signifying ABA and glucose as negative regulators, whereas ROS, riboflavin and mitochondrial complex IV as positive regulators. Gene expression analysis of α-amylases revealed H2O2 supplementation mimicked aerobic gene expression pattern. Plausible mechanisms of riboflavin and H2O2 function in submergence tolerance were also discussed. Finally, we isolated a novel mutant of Rayada variety with Kaladigha background and having four interesting phenotypes of practical implications. Mutant plant shows purple pigmentation throughout the plants organs along with dense and elongated trichomes on the adaxial leaf surface. In addition, the same mutant also shows high frequency of stigma exsertion. But ultimately, we observed that the mutant plant is completely sterile. The possible reason of the sterility was found being related to the stigma receptivity. Severe reduction of ROS accumulation in stigmas of mutant plant was observed after fluorescent H2DCF-DA staining. However, pollen grains are completely viable with normal shape and size. Interestingly, the fertility was partially restored after humidifying the panicles. Mutant progeny showed dense black coloration in seeds with significant reduction of grain weight. Moreover, it showed segregating ratio of 3:1 for purple pigmentation, suggesting single gene mutation nature. Other phenotypic features confirmed the mutant as a Rayada variety with Kaladigha background, not a seed contamination. After extensive data mining of these four phenotypes, we identified maize Lc gene with three similar phenotypes reported earlier excluding stigma exsertion, hence considered as candidate gene of this mutant. The gene expression of maize Lc homolog of rice, OsbHLH13, was exceptionally up-regulated in the purple mutant. Further studies of genetic characterization may open up the practical implications of this mesmerizing mutant. In summary, Rayada is a primitive deepwater rice ecotype that can offer many traits and genetic resources that are badly needed in rice breeding for stress tolerance and the time is mature to do the more detailed research with rapid advances in genome research weaponry

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Rice (Oryza sativa L.) that is grown in the U.S. is predominantly grown in the mid-south. Current Mississippi State University recommendations for nitrogen (N) fertilization of rice suggest a single application of 168 kg N ha-1 on soils with CEC ¡Ü 20 and 202 kg N ha-1 on soils with CEC > 20. The primary objective was to identify alternative N management strategies that may potentially be used to reduce costs associated with aerial application of N fertilizer to rice. Research was established at the Delta Research and Extension Center, at Stoneville, MS, on two soil textures during 2015 and 2016. The combination of application timings and N sources resulted in a total of eight N management strategies. Data from all siteyears were pooled together for analysis to evaluate differences among N management strategy. Urea + [N-(n-butyl)thiophosphoric triamide] (NBPT) applied in a single application 7 days before flood (DBF), two-way split application, and PCU-2 LF produced statistically similar and greatest mean rice grain yield. These data suggests that N fertilizer can be applied early (2 to 3 leaf growth stage) from a ground based fertilizer spreader prior to the levee construction. Single optimum and two-way split N management strategies produced more total dry matter (TDM) at heading (HDG) and more N uptake at HDG. Urea + NBPT applied in a single application 7 DBF should be the N management strategy of choice in mid-southern U.S. rice production.

Weedy red rice is conspecific weed of rice, identified as a threat to global rice production. As weedy rice is more tolerant to stresses than cultivated rice and has wide genetic and morphological variation we hypothesized that weedy rice has high herbicide tolerance and weed suppressive potential. Herbicide tolerance and weed suppressive potential of 54 weedy rice accessions were evaluated and the traits were associated with molecular markers. Accessions B2, B20 and S11 showed high tolerance to glyphosate and B49, B51 and S59 had high tolerance to flumioxazin. All the accessions were controlled 100% with 1311g a.i/ha (1.5x) rate of glufosinate. Accession B2 inhibited the growth of barnyardgrass and amazon sprangletop by more than 50% indicating its high weed suppressive potential. Nei’s gene diversity and Shannon’s information index among the weedy rice accessions were found to be 0.45 and 0.66 respectively indicating high genetic diversity among weedy rice accessions.

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Thesis advisor: S. Anukriti / I examine how increases in the tariff rate impacted market prices and household consumption of imported rice in Nigeria during 2001-2018. I find that the country-level tariff pass-through for imported rice was 7 percent and occurred three-months after implementation. When faced with increases in the tariff-rate, households decrease their consumption of imported rice. Households that face greater exposure to the tariff rate decrease their consumption more than those that are less exposed. The relatively small tariff pass-through and the responsiveness of consumption to increases in the tariff rates are crucial pieces of information for informing Nigeria’s future rice policy. / Thesis (BA) — Boston College, 2019. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Departmental Honors. / Discipline: Economics.

Weedy rice is of the same species as cultivated rice, Oryza, and is a common rice weed exhibiting allopathic characteristics. Incorporation of allelopathic traits from weedy rice into cultivated rice may have a positive impact on rice yield. The overall objective of this study was to characterize weedy rice accessions based on the allelopathic potential to suppress barnyardgrass. These accessions, once discovered, may be used in identifying phenotypic traits and genes associated with their weed suppressive trait. Ten weedy rice accessions, and five rice cultivars (Rex, CL163,Rondo, PI312777, PI338046) were screened using a stair-step technique. The allelopathic potential was calculated based on the percent inhibition of barnyardgrass. The best performing accessions were phenotyped for root characteristics in a lab setting. Lastly, 30 SSR markers were used to evaluate the weedy rice to identify markers associated with the trait. Accessions identified in this study should be considered in the development of weed-suppressive rice cultivars.

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