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Sweetpotato storage roots are subjected to several forms of post harvest spoilage in the tropical climate during transportation from farmers' field to market and in storage. These are due to mechanical injury, weight loss, sprouting, and pests and diseases. Sweetpotato weevil is the single most important storage pest in tropical regions for which no control measures or resistant variety are yet available. Several microorganisms (mostly fungi) have been found to induce spoilage in stored sweetpotatoes. The most important among them are Botryodiplodia theobromae, Ceratocystis fimbriata, Fusarium spp., and Rhizopus oryzae. The other less frequently occurring spoilage microorganisms include Cochliobolus lunatus (Curvularia lunata), Macrophomina phaseolina, Sclerotium rolfsii, Rhizoctonia solani, Plenodomus destruens. Microbial spoilage of sweetpotato is found associated with decrease in starch, total sugar, organic acid (ascorbic acid and oxalic acid) contents with concomitant increase in polyphenols, ethylene, and in some instances phytoalexins. Several methods are used to control microbial spoilage. Curing to promote wound healing is found as the most suitable method to control microbial spoilage. Curing naturally occurs in tropical climates where mean day temperature during sweetpotato harvesting season (February-April) invariably remains at 32-35 degrees C and relative humidity at 80-95%. Sweetpotato varieties varied in their root dry matter content, and low root dry matter content attributed for their high curing efficiency. Curing efficiency of varieties also differed in response to curing periods. Fungicide treatment, bio-control, gamma irradiation, hydro warming, and storage in sand and saw dust were found to have intermediate impacts in controlling spoilage and enhancing shelf life of sweetpotato roots. Breeding program has to be chalked out to develop new varieties suitable to curing under tropical conditions in addition to developing varieties having multi-spectrum resistance to major post harvest rot pathogens and sweetpotato weevils.

Storage root formation and development in sweet potato [Ipomoea batatas (L) Lam. Convolvulaceae] is a complex process characterized by the cessation of root elongation, genesis of vascular cambium, anomalous and interstitial cambia, and increase in radial growth by increased cell proliferation and expansion concomitant with the massive deposition of starch and storage proteins that eventually result in storage root enlargement. Phytohormones play a crucial role in the formation of storage roots. Three class I knotted-like homeobox (KNOX1) genes-SRF1, SRF5, and SRF6-modulate carbohydrate metabolism and cell division. The genes Ibkn1 and Ibkn2 activate cytokinin biosynthesis. Transcription factors derived from MADS box genes IbMADS1, IbMADS3, IbMADS4, and IbAGL17 induce signal transduction pathway leading to storage root formation and development. The occurrence of SRD1 transcripts mainly in the actively dividing cells, including the vascular and cambium cells, and the increase in endogenous indole-3-acetic acid (IAA) content and three auxin-inducible AUX/IAA gene transcripts concomitantly with SRD1 transcripts suggest the involvement of SRD1 during the early stage of storage root development. Along with IbMADS1 induction, two storage root marker genes, which encode a major storage protein sporamin and IbAGPase that encodes AGPase for ADP-glucose production in starch biosynthesis, are up-regulated during the early period of storage root development. A class III HD-Zip protein 8 regulating the development of cambia and secondary vascular tissues, a short-root protein that is a key regulator in root 157 radial patterning, meristem maintenance, and asymmetric cell division, the expansin gene IbEXP1 encoding a cell wall loosening protein, genes encoding cyclin A-and cyclin D-like proteins, and five cyclin-dependent kinases are upregulated during storage root formation. Genes encoding ADP-glucose pyrophosphorylase, granule-bound starch synthase, starch synthase, and phosphoglucomutase are up-regulated, whereas genes encoding pyruvate decarboxylase and lactate dehydrogenase are down-regulated during storage root development. The endogenous sucrose levels influence the expression of two AGPase isoforms: ibAGP1 and ibAGP2. The expression of cell wall-bound (extracellular/apoplast) acid invertase activity gene (cwINV) predominates during early period, whereas the expression of cytosolic activity of sucrose synthase gene (SuSy) predominates during later period of storage root enlargement. The competition between lignification and formation of anomalous cambia and the associated starchaccumulating cells determine storage root development. Genes encoding enzymes such as coumaroyl-CoA synthase, caffeoyl-CoA O-methyltransferase, and cinnamyl alcohol dehydrogenase during storage root formation reduce lignification in tissue sections of storage roots.

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Knowledge‐intensive approaches have been proposed to manage the variability in indigenous nutrient supplies (IS) in irrigated rice (Oryza sativa L.) systems. On‐farm experiments were conducted at 155 locations in seven domains of Asia to quantify the variability of soil properties, grain yield, and nutrient uptake in N, P, and K omission plots (0‐N, 0‐P, and 0‐K, respectively). Except for pH, coefficients of variation of soil properties within a domain ranged from 17 to 43%. Similar ranges were measured for grain yield and plant nutrient uptake in nutrient omission plots, which served as crop‐based estimates of indigenous N, P, and K supply. Soil properties showed little association with plant nutrient uptake or grain yield in nutrient omission plots. Mean grain yields in nutrient omission plots increased in the order 0‐N (3.9 Mg ha−1) < 0‐K (5.1 Mg ha−1) ≤ 0‐P (5.2 Mg ha−1). Soils, climate, and crop management caused large variability of IS among irrigated rice domains, years, growing seasons, and fields within a domain. Grain yield and nutrient uptake in omission plots were mostly higher in high‐yielding than in low‐yielding climatic seasons. No changes in indigenous N supply occurred for periods of 4 to 6 yr in the same seasons. Grain yields in nutrient omission plots were strongly correlated with each other and also with the yield in the fertilized farmers' fields. Fertilizer recommendations should be fine‐tuned to spatial domains with relatively uniform agroecological characteristics, cropping practices, and socioeconomic conditions. Within such domains, season‐specific management of the IS variability can include field‐specific approaches.