Selection of desirable phenotypes and characterization of variability in economically important traits are essential for domestication of indigenous fruit trees (IFTs). Currently, participatory tree selection is a widely accepted approach in IFT domestication wherein farmers' knowledge and preferences are included in tree selection processes. In Arunachal Pradesh, India, fruits of Phoebe cooperiana are extensively consumed by people and traded across the state. In this study, we employed a selection index to screen trees for superior fruit traits from a base population of 45 farmer-identified trees of P. cooperiana in Arunachal Pradesh. Based on fruit diameter length ratio, pulp fruit ratio and yield, 19 trees were selected for superior fruit traits. The per cent improvement for 10 fruit and seed traits ranged from 0.16 to 14.56% compared to the base population. Significant variation for all fruit and seed parameters was observed among the 19 trees with coefficient of variation values ranging between 1.92% for fruit diameter and 8.26% for seed weight. There was significant positive association between economic traits including fruit weight with pulp weight, fruit diameter length ratio with fruit weight and pulp thickness with pulp weight. Principal component analysis revealed that variability was largely contributed by fruit weight (0.49), pulp weight (0.46), seed weight (0.45) and fruit diameter (0.42). Cluster analysis grouped phenotypes into seven groups with no clear clustering of individuals from the same area. The study highlights the significance of participatory tree selection approach and the benefits of individual tree selection in capturing wider variation and locating extreme phenotypes in IFT domestication.

A low-cost technique named ‘on-farm’ seed priming is increasingly being recognized as an effective approach to maximize crop establishment. It consists of anaerobically soaking seeds in water before sowing resulting in rapid and uniform germination, and enhanced seedling vigour. The extent of these benefits depends on the soaking time. The current determination of optimal soaking time by germination assays and mini-plot trials is resource-intensive, as it is species/genotype-specific. This study aimed to determine the potential of the seed respiration rate (an indicator of metabolic activity) and seed morphological changes during barley priming as predictors of the priming benefits and, thus, facilitate the determination of optimal soaking times. A series of germination tests revealed that the germination rate is mostly attributable to the rapid hydration of embryo tissues, as the highest gains in the germination rate occurred before the resumption of respiration. Germination uniformity, however, was not significantly improved until seeds were primed for at least 8 h, that is, after a first respiration burst was initiated. The maximum seedling vigour was attained when the priming was stopped just before the beginning of the differentiation of embryonic axes (20 h) after which vigour began to decrease (‘over-priming’). The onset of embryonic axis elongation was preceded by a second respiration burst, which can be used as a marker for priming optimization. Thus, monitoring of seed respiration provides a rapid and inexpensive alternative to the current practice. The method could be carried out by agricultural institutions to provide recommended optimal soaking times for the common barley varieties within a specific region.

The current study was conducted in 2013 to identify the seeds of three species of Amaranthus, Amaranthus viridis L., Amaranthus retroflexus L. and Amaranthus albus L., by using the artificial neural network (ANN) and canonical discriminant analysis (CDA) methods. To begin with, photographs were taken of the seeds and 13 morphological characteristics of each seed extracted as predictor variables. Backward regression was used to find the most influential variables and seven variables were derived. Thus, predictor variables were divided into two sets of 13 and seven morphological characteristics. The results showed that the recognition accuracy of the ANN made using 13 and seven predictor variables was 81.1 and 80.3%, respectively. Meanwhile, recognition accuracy of the CDA using the seven and 13 predictor variables was 74.0 and 75.7%, respectively. Therefore, in comparison to CDA, ANN showed higher identification accuracy; however, the difference was not statistically significant. Identification accuracy for A. retroflexus was higher using the CDA method than ANN, while the ANN method had higher recognition accuracy for A. viridis than CDA. In addition, use of 13 predictor variables yielded a greater identification accuracy than seven. The results of the current study showed that using seed morphological characteristics extracted by computer vision could be effective for reliable identification of the similar seeds of Amaranthus species.

There are a number of studies describing the gross range of morpho-anatomical variability in epiphytic Tillandsia species, but the interspecific variation in seed traits remain largely unexplored, although these play an important role in determining dispersal and establishment success. In order to evaluate interspecific variation in seed morphology, anatomy and germination, we sampled six Tillandsia species from the Yucatan peninsula, Mexico, distributed along a precipitation gradient. We studied morpho-anatomical traits (seed length, seed mass, ratio of coma to seed, ratio of embryo to endosperm), seed terminal velocity in still air, and performed histochemical analyses and germination trials under controlled conditions. Tillandsia recurvata differs from the other five species in the structure of the plumose coma; it was the only species lacking an endosperm and showed distinct seedling development. Among the species, bigger seeds were related to longer comas, and had higher germinability. Overall, seed terminal velocity was invariably slow, compared with reports of other anemochorous species, suggesting a high dispersal potential. Taxonomical and ecological implications of our results are discussed.

Seed heteromorphism is the formation of different seed morphs from the same individual. Two seed morphs have been preliminarily observed in Leptocereus scopulophilus. One morph shows an apparent natural scarification of its coat. Herein we describe the seeds, taking into account shape, coat integrity, surface, dimensions, mass and the position of germination cracks. We defined two seed morphs using the integrity of the spermoderma: fragmented seed coats (FSC) and complete seed coats (CSC). We also evaluated minimum germination time, germination rate and germinability. The seed morphs did not differ significantly in traits; however, regular striations along the cuticle of the periclinal walls were more visible in the FSC compared with the CSC. Both seed morphs displayed anticlinal cell boundaries in the border region that are channelled and straight in the dorsal-ventral region but difficult to define in the lateral region. We found four morphological variations in different positions where the radicle or cotyledons emerge and variations in cuticle thickness in different regions of the seed that could determine the formation of cracks during germination. All germination variants occurred in both seed morphs, albeit in different proportions. Germination was higher and faster for the FSC compared with the CSC. These germination differences could be related to a thinner cuticle in the FSC and the punctual release of its spermoderma, which facilitates a quick imbibition of the embryo and the breaking of the seed coat. Our results indicate that differences in germination parameters between the two seed morphs relate to differences in the percentage of dormant seeds, which favour the temporal expansion of germination and reduce competition between siblings. To propagate the species for conservation purposes, we recommend using FSC, while CSC may be used to establish a seed collection ex situ.

Giant ragweed exhibits a high degree of polymorphism among individual plants in seed size, shape, spininess, and color. These features may play an important role in giant ragweed seed survival and predation avoidance; however, they are difficult to evaluate because of lack of quantification methods. A computer imaging technique was developed for describing and classifying giant ragweed seeds using digital images of the seed top and side views. Seed samples collected from 20 different giant ragweed plants (classes) were mounted and digitally scanned. Quantitative features were extracted from the seed images, including color, width, height, area, and seed perimeter. A polygon (convex hull) of the seed image based on the seed outline was constructed, from which spininess indices were developed. Fisher's linear discriminant with normalized nearest neighbor classification was used to classify randomly selected images of individual seeds according to class (maternal origin), using the extracted features as a database. The best classification rate achieved was 99%, with 138 out of 140 seeds correctly matched using data from both the top and side views. Seed features were easily extracted and varied from 1.2- to 4.5-fold among classes. Area and perimeter measurements varied least within classes but varied most among classes, suggesting that these features discriminate effectively among seeds from different plants in giant ragweed. Convex hull area : seed area ratio, using the seed top view images, was the best index of seed spininess, aligning well with visual assessment and providing greatest discrimination among classes. This experiment shows that in the case of giant ragweed, seeds from different plants are distinguishable in an objective and quantitative manner. This imaging technique can be applied to identification of seeds from different species and to studies on variable seed morphology within a species.

Theoretical models predict that seed size and seed-bank persistence evolve interdependently, such that strong selection for one trait corresponds with weak selection for the other. This framework has been supported and rejected by empirical data, and thus, conclusive evidence is lacking. We expanded the seed size–persistence framework to include seed-coat thickness, a defence trait previously correlated with seed survival in soil. To do this, we used Abutilon theophrasti accessions with varied evolutionary histories and we quantified associations among seed traits including morphology, size, coat thickness, dormancy (percentage of viable seeds that fail to germinate under optimum conditions) and seed-bank persistence (percentage of viable seeds remaining after 1 year of burial). Statistical models were developed to test the hypothesis that combined measurements of seed-coat thickness and seed size better explain variability in seed-bank persistence than seed-size data alone. Results indicated that measurements of seed size (length, width, mass) were negatively correlated with coat:width ratio (coat thickness relative to seed width) and coat:mass ratio (coat thickness relative to seed mass). Accessions characterized by smaller seeds with proportionally thicker seed coats were more dormant and more persistent in soil than accessions characterized by larger seeds with proportionally thinner seed coats. Seed-coat thickness data improved the explanatory power of logistic regression models for seed-size effects on both seed-bank persistence and dormancy. These results indicate that supplementing seed-size data with seed-defence data may clarify previously reported contradictory results regarding trade-offs between seed size and seed-bank persistence.

The wind dispersal of a plant propagule is likely to be improved by any structure that increases air resistance, e.g. the pappus of the achene of Asteraceae, the wings of Acer or dipterocarp fruits, or the plumose seed appendage which is characteristic of species of the subfamily Tillandsioideae in the Bromeliaceae. Not surprisingly then, promotion of airworthiness is usually assumed to be the primary function of this so-called ‘coma’ found in epiphytic Werauhia, Tillandsia, Guzmania or Catopsis species (Benzing 1980, 2000). However, the diverse structure of coma hairs with bifurcate cross-walls or hooks also assists in sticking to rough surfaces, such as tree bark and rocks, which indicates another important function: keeping seeds in place until germination and the development of roots (Benzing 2000, Palací et al. 2004). Multiple rather than singular functions of seed plumes or pappi have also been shown for soil-rooted plants in other plant families, where these structures are not only highly efficient for wind dispersal, but also for attachment to animal fur (Couvreur et al. 2004).

A critical analysis of different criteria used in investigating seed diversity was made. It is concluded that the most promising way to understand the evolution of seeds is to study not only their morphological features, as used by most workers in the field, but also the physiological diversity of seeds in connection with the taxonomic system of plants, together with their ecological and geographical peculiarities.