Rayada specialty: the forgotten resource of elite features of rice

Abstract

Crop domestication and thereafter gradual selection or directional breeding have narrowed the genetic diversity of elite varieties and even promoted gathering of deleterious mutations in their stress response mechanisms, whereas local ecotypes, landraces and wild relatives still growing on native environment and preferences keep the genetic diversities for features like stress tolerance. 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. Tolerance to prolonged flood, submergence and cold are special features along with strong photoperiod sensitivity and lack of dormancy. Moreover, longer root system and prompt recovery capacity make it as an elite resource of stress tolerance. However, it has long been neglected because of mainly its long life cycle and poor yield. This review examines the specialty of Rayada rice and the potential use of its unique traits.

Figure 1

Status of deepwater rice cultivation in Bangladesh. Comparative scenario of cultivation area (a) and average yield (b) of deepwater (DWR) and total rice cultivation in Bangladesh from 1971–72 to 2005–06.

Figure 2

Climatic features of Rayada growing areas. a) average rainfall, b) humidity and c) lowest and highest temperature. Long term (1948–2008) average climatic status of Rayada growing area was calculated based on data of two nearby weather stations (Faridpur and Jessore) of Rayada grown area. Metrological data were collected from Bangladesh Agricultural Research Council website ( http://www.barc.gov.bd/data_stat.php).

Figure 3

Internode elongation pattern of Rayada variety, Kaladigha to typical deepwater rice and comparative phenotypes of Rayada after inundation. (a) internode elongation pattern Rayada and typical deepwater rice (Habigonj amam I-VIII after Hasanuzzaman ( 1974) (bar = SD), (b) number of internodes per plants, (c) phenotypic comparison of basal internodes (above soil) in Rayada in control and inundated condition (bar = 5 cm), (d) comparative phenotypes BRRI52, Kaladigha, and inundated Kaladigha (left to right, respectively) at plants maturity. Plants (4.5 months old) were grown in water tube with increasing water level keeping top leaves above water for 45 days reaching 2.5 meter. Then the plants were kept under around 2.5 meter inundation (water renewal fortnightly) for rest of months (around 7 months) till seed mature. Basal internodes/nodes (3–4) beneath the soil were excluded in estimation and comparison.