Dr. Nandkumar M. Kamat
Along the saline margins of the Chapora estuary survives an old Goan winter cowpea locally known as alsande black-eyed pea or Vigna unguiculata subsp. unguiculata. For generations, farmers in Revoda have cultivated this crop on small floodplain farms exposed to tidal influence, salt stress, and seasonal moisture fluctuations. However, almost no modern scientific work has been conducted on Revoda traditional cultivar. This gap prompted me to undertake a detailed investigation of its seeds using digital image analysis, morphometry, chromotyping, and statistical methods. What emerged from the study was not merely a description of a local bean but evidence of a complex, still unresolved evolutionary story.
The farms close to estuary where alsande is grown are ecologically unusual. During the dry months, from December to May, the salinity in the surrounding environment can increase considerably. Farmers reported that the crop matures in approximately 30 days and survives without supplemental irrigation, relying largely on residual post-monsoon soil moisture in sandy-silty soil. As a scientist, I began to ask questions. Could such an environment have shaped the seed characteristics of this landrace over the generations? Did long exposure to saline-drought stress select certain seed traits? Was this apparently simple traditional crop a biologically heterogeneous population with multiple morphotypes?
To investigate these questions, I studied a bulk lot of approximately 1,100 seeds, along with a carefully selected random sample of 100 seeds. This study combined digital photography, image analysis, biomass measurements, and statistical analysis. The first stage involved high-resolution imaging of the target area. The bulk seed lot spread on a tray was photographed, and 100 seeds were individually arranged in a 10×10 grid on a black acrylic background under diffuse daylight using a Samsung Galaxy S24 smartphone.
The most innovative part of the study involved digital chromotyping, a technique I developed at Goa University in 2005 to study biological specimens ranging from microbial colonies and mushrooms to Baltic amber, and which my students used to publish research papers. In ordinary language, this means scientifically studying seed colour patterns using computer-based image analysis rather than relying only on human visual impressions.
At first glance, many seeds appear superficially similar. However, once analysed digitally, the hidden diversity became astonishing. The bulk seed lot was resolved into 12 major colour groups and 88 individually named colour entries. Even the smaller 100-seed sample produced 15 colour groups and 74 named colour entries in the database. This is important because highly uniform crop varieties generally exhibit limited chromatic diversity. In contrast, traditional farmer-maintained landraces often exhibit greater variability. Revoda alsande clearly belonged to the
second category.
The dominant colour category in both analyses was orange and brown. In the bulk lot, this constituted 68.94% of the chromatic mass, whereas in the 100-seed sample, it increased to 80.84%. The dominant individual colours included shades described digitally as fawn, copper, bronze, burlywood, desert and Indian yellow. To ordinary readers, these names may sound artistic, but scientifically, they represent quantified colour signatures derived from numerical pixel data. Such colour differences can reflect variations in pigmentation chemistry, seed coat structure, maturation history, or underlying
genetic differences.
One particularly striking result was the presence of many rare colour variants. Approximately 45.5% of the colour variants in the bulk sample occurred at very low frequencies. In evolutionary biology, this type of long tail of rare variants is often associated with heterogeneous populations rather than highly standardised crop lines. This suggests that the population may still maintain hidden diversity rather than collapsing into complete uniformity.
Biomass analysis provided another important clue. The mean individual seed mass was approximately 216 mg. These seeds are unusually large for cowpeas. The study compared the value with standard improved cowpea reference values and found that Revoda alsande exceeded the midpoint of those improved varieties by more than 144%. Why might larger seeds be important in such environments? Large seeds contain more food reserves. Under saline or drought-prone conditions, seedlings from larger seeds may have greater survival capacity because they have greater carbohydrate, protein, and mineral reserves during the critical early stages of germination and establishment. This led us to formulate an evolutionary hypothesis. Over many generations, the harsh saline-drought environment of the estuarine floodplain may have favoured plants that produced larger, high-reserve seeds. Farmers may have unconsciously selected more vigorous seed types for cultivation, resulting in gradual phenotypic differentiation shaped jointly by environmental stress and farmer selection.
The average seed dimensions converged to approximately 9 mm in length, 7 mm in width, and 5 mm in thickness. Most seeds displayed a kidney-oval shape. Statistical analysis showed that the majority belonged to the medium-width category, although smaller and larger forms also existed. The most fascinating result emerged when the three independent analytical systems converged on the same conclusion. Chromotyping identified a dominant morphotype, accounting for approximately 45% of the population. Biomass analysis independently identified a medium-weight class, constituting approximately 45%. Morphometric analysis simultaneously identified a dominant medium-width class.
This three-way convergence is highly significant. When entirely independent methods repeatedly point to the same dominant phenotype, the probability of random coincidence decreases sharply. This evidence strongly suggests the existence of a primary morphotype within the Revoda alsande population. The primary morphotype can be described approximately as follows: medium-mass seeds, warm orange-tan seed coat, kidney-oval shape, and relatively large dimensions.
Simultaneously, secondary and tertiary morphotypes appeared repeatedly in the data. Some seeds were dark copper-bronze. The others were smaller and redder. This recurring structured variation suggests that the landrace may represent a biologically mixed population rather than a single genetically uniform cultivar. This is where the “evolutionary mystery” truly begins for us. Who shaped this population? Nature alone? Farmers alone? Or both together over the centuries?
Traditional agriculture often operates as a long-term evolutionary partnership between humans and the environment. Farmers save seeds from desirable plants for future use. Environmental stress eliminates weaker forms. Over generations, populations gradually change, even without formal scientific breeding programmes, and the Revoda alsande appears to preserve traces of this process, with the estuarine environment itself functioning as a natural selection filter. Salinity, water stress, and tidal influence continuously challenge plants. Under such conditions, maintaining multiple phenotypes may be advantageous because environmental conditions fluctuate from season to season. Some variants may tolerate higher salinity levels. Others may germinate more efficiently than others. Some plants may survive drought stress better than others. Diversity can serve as biological insurance. This is particularly relevant today because climate change is increasing salinity intrusion and environmental instability in many coastal agricultural regions. Modern agriculture often values genetic uniformity because it simplifies both cultivation and marketing. However, ecological resilience frequently depends on diversity. Traditional landraces sometimes preserve adaptive traits that are neglected or lost in industrial agriculture. Revoda alsande may therefore represent more than a local food crop. This may contain valuable adaptive biological information relevant to future climate resilience in coastal agriculture.
However, many important questions remain unanswered. The present study focused mainly on seed morphometry, chromotyping, and statistical structure. Future studies should include germination studies under salt stress, physiological experiments, and molecular genetic analyses. Only then can the hidden biological architecture of this remarkable landrace be fully elucidated. However, even at this stage, one conclusion is already clear. The humble alsande cultivated quietly for generations in Revoda is not an ordinary bean population. Beneath its simple appearance lies evidence of phenotypic diversity, environmental adaptation, and possible ongoing evolutionary differentiation shaped by one of Goa’s most challenging agricultural landscapes.
