Problem: Kernel cracking due to field fissuring is one of the leading causes of reduced milling quality in rice. Any reduction in fissuring will result in direct increases in whole-kernel yield and profit for both the producer and the miller. The rice industry experienced this increased profitability first hand when producers grew the fissure resistant variety ‘Cypress’ after its release in 1993. Breeders want to develop new, improved varieties with fissure resistance equal to Cypress’, but progress is severely limited by the fact that present methods for evaluating fissure resistance all require large amounts of seed and/or labor. The presently available evaluation techniques may be used to prevent the release of a highly susceptible variety, but they cannot be used to proactively select for high fissure resistance among segregating breeding progeny.

Research Objective & Approach: Drs. Shannon Pinson (USDA, Beaumont, TX) and Scott Osborn (U. of AR) have joined together their Genetics and Ag. Engineering expertise to study genetic, physical, and chemical grain attributes (Fig. 1) with the aim of identifying key factors that could then be used by breeders to identify fissure resistance among segregating progeny. This research has received support from TRRF and the Rice Foundation.

Engineers studying post-harvest fissuring during drying and storage have identified a multitude of kernel components, such as hull chemistry and tightness, bran chemistry and thickness, and endosperm chemistry and shape, as affecting fissure rates (Fig. 1). Before Drs. Pinson and Osborn could identify which of these factors were key determinants of pre-harvest fissuring, they first had to develop a “measuring stick” capable of distinguishing both large and small differences in fissure response. At the initiation of this project, it was known that Cypress was more fissure resistant than ‘Lemont’, and it was suspected but not proven that ‘LaGrue’ and ‘TeQing’ were less fissure resistant than Lemont. Pinson’s and Osborn’s replicated multi-year milling stability data now document that the order of fissure resistance among the following varieties is ‘Saber’ > ‘Cypress’ > ‘Jodon’ = ‘Cocodrie’ = ‘Lemont’ = ‘LaGrue’ > ‘TeQing’ > ‘Jefferson’. ‘Saber’ consistently exhibited fissure resistance equal to or better than that of Cypress.

Dr. Key Findings and Future Research Directions:

Field studies focussed on fissuring should be planted after May 5. Fissure-causing environments are more prevalent later in the growing season, making plots planted early in the season less informative than plots planted later in the season. Cypress’ fissure resistance is predominantly due to the hull barrier. When the hull keeps moisture out of the kernel, less swelling and pressure occurs within the kernel. If the underlying causes of Cypress’ low moisture transfer through the hull (i.e., hull tightness versus permeability) are identified, they may then be exploited as rapid, small-sample methods for identifying fissure resistance among breeding progeny. Saber’s fissure resistance appears to be predominantly due to endosperm characteristics. High endosperm diffusivity allows both moisture and pressure to spread through the kernel rather than being concentrated, decreasing the likelihood of kernel fissuring. It may be possible to create varieties with even higher levels of fissure resistance by combining key attributes from Saber with those of Cypress.

Figure 1 describes the properties studied by Pinson and Osborn to determine their relative importance to fissure resistance. Properties determined to be significantly associated with fissure resistance/susceptibility are shown in red, factors determined to not have a strong impact on fissuring are in blue, factors not yet evaluated are in black

Technicians in the USDA Rice Genetics project are Faye Seaberg, Piper Roberts and Josh Burrows. For more information, contact Dr. Shannon Pinson by phone at 409.752-5221 ext. 2266 or email spinson@ag.tamu.edu .