Serology and Species Relationships in Annual Bromes (Bromus L. sect. Bromus)

Abstract

The subsectional classification of Bromus section Bromus based largely on morphological evidence, is reviewed. Morphological features of taxonomic value in the group are discussed in terms of natural variation and behaviour under artificial cultivation. A classification is presented based on the most reliable and predictive of these features and the bearing of evidence from geographical distribution, karyology, and cytogenetics is considered. There is incomplete correlation between the evidence from these diverse fields. A serological inquiry is described. The interpretation of different types of serological evidence is discussed. The results of the work show general support for the morphological scheme presented, but there are a number of anomalies and discrepancies. These are fully considered and related to the other types of taxonomic evidence available. The serological findings are used as a guide to the reconstruction of the original classification. It is shown that B. arvensis and B. brachystachys are highly likely to be ancestral to two closely related groups of Eurasian tetraploid species which are defined. A third diploid, B. scoparius, or a very close relative, is also probably implicated. The serological similarity of B. arvensis and B. brachystachys additionally provides an explanation, supposing them to be ancestral diploids, for a previously demonstrated serological similarity of the morphologically distinctive tetraploids B. hordeaceus and B. lepidus. Two diploid taxa of unexpectedly low serological affinity are indicated. The results support the idea that the B. pectinatus-complex may be of intersectional amphidiploid origin. A chart summarizing species relationships, taking into account the new serological results, and a table of the revised classification, are presented. The potential of the method as a cheap and rapid screening technique for diploid ancestors in studies of cereal grasses and other crops is commented upon.