Study of Flowering Pattern in Setaria viridis, a Proposed Model Species for C4 Photosynthesis Research

Hindawi Publishing Corporation Journal of Botany Volume 2013, Article ID 592429, 7 pages http://dx.doi.org/10.1155/2013/592429 Research Article Study of Flowering Pattern in Setaria viridis, a Proposed Model Species for C4 Photosynthesis Research Govinda Rizal, Kelvin Acebron, Reychelle Mogul, Shanta Karki, Nikki Larazo, and William Paul Quick C4 Rice Center, International Rice Research Institute, DAPO 7777 Metro Manila, Philippines Correspondence should be addressed to William Paul Quick; Received 29 July 2013; Accepted 3 September 2013 Academic Editor: Karl Joseph Niklas Copyright © 2013 Govinda Rizal et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Green foxtail millet (Setaria viridis) has NADP-ME type of C4 photosynthesis. Because of its short life cycle, small genome size of ∼515 Mb, small plant stature, high number of seed set, simple growth requirements, and wide adaptability, this diploid (2𝑛 = 18) weed is proposed to be a model species for the study of C4 photosynthesis. It is also a representative of bioenergy grasses and a model for genetic study of invasive weeds. Despite having all traits of a model species, it is difficult to cross-pollinate because its flowering behavior is not well studied. We used time lapse digital recording to study the flowering time and pattern along a single panicle. We found that flowering in Setaria was triggered by the darkness of the night and when the temperature was lower than 35∘ C. The anthesis of all the spikelets in a panicle took up-to three nights flowering from 9:30 pm to 10:00 am in the morning. Each spikelet has three phases of anthesis during which pollination occurs. A spikelet remains open for less than three hours. The pollination time for each spikelet is less than 60 minutes. Information from this study will facilitate the geneticists and plant breeders to plan for efficient crossing of Setaria. 1. Introduction A common weed, green foxtail millet (Setaria viridis (L.) P. Beauv.), which belongs to family Poaceae, has gained the attention of plant scientists due mainly to its inherent C4 traits. Brutnell et al., (2010) proposed to make this weed a model species for C4 photosynthesis research [1], and there is a progressive support and acceptance to the proposal [2, 3]. About 125 species are identified under genus Setaria [4], and S. viridis is considered the ancestral stock of this genus. Allozyme assay has shown that foxtail millet (S. italica) was the domesticated form of the S. viridis [5]. S. italica was grown as early as 6,000 years ago and was one of the oldest cultivated cereals of China [6]. Today, several species of millet belonging to the family Poaceae are widely cultivated. The major cultivated species of millet include: Pennisetum glaucum (pearl millet), Setaria italica (foxtail millet), Panicum miliaceum (proso millet), and Eleusine coracana (finger millet) [7]. The green foxtail millet is an invasive weed because of its short life span and its ability to produce seeds with long life [8]. Recently, it was reported that S. viridis also showed repeated evolution to herbicide resistance [9]. This finding opens a new dimension to uncover the genetic basis of the evolution of herbicide resistance. A model plant species should have rapid regeneration cycle, small genome size, small plant size, plenty of seeds, propagation through seeds, easy to grow, and wide adaptability. It meets all these traits. A model plant should also be easy to cross pollinate to develop different kinds of mapping and breeding populations. However, the crossing of Setaria is not easy. It is important to understand the flowering pattern of S. viridis to use them for crossing and to generate recombinant populations. The onset of flowering marks the transition from vegetative to reproductive phase in plants and is a necessary characteristic of bisexual plants. The objective of this research was to study the flowering pattern, flowering time, and flowering period among different Setaria accessions in general 2 and the model accession A10.1 in particular that was grown in natural or close to natural environmental conditions. The mechanism of opening and closing of flowers is reviewed by van Doorn and van Meeteren [10]. Mauro-Herrera et al., (2013) had studied the genetic control of flowering in Setaria and reported three genes for flowering time in maize colocalized with the QTL they identified for Setaria [3]. The molecular-genetic studies of these populations can shed light on the mechanism of evasiveness of weeds and possibly lead to discovery of effective strategies of weed control. The temporal and spatial behaviors of opening of flowers in Setaria are reported here. This information is useful in producing crossed populations of this proposed model for the C4 species. 2. Materials and Methods Fifteen accessions of S. viridis were obtained from North Central Regional Plant Introduction Station of the United States Department of Agriculture. These seeds were grown at Los Banos, Philippines. The accessions included one each from Afghanistan, Canada, and Chile, two each from China and Russia, three from Iran, and five from Turkey. Their accession number, region of origin and other traits are given in Tables 1 and 2. One hundred seeds of each accession were grown in green house conditions to study the phenotypic variations. Prior to sowing, the seeds were incubated at 45∘ C for five days to break the seed dormancy. Then, the seeds were soaked in distilled water and allowed to germinate overnight at room temperature. Germinated seeds were sown into sterilized soil in pots. The sterilized soil contained 75% garden soil and 25% river-sand and fertilized with 14-14-14 NPK at the rate of 0.25 g⋅kg−1 of soil. The seedlings grown in the pots were dipped into nutrient solution everyday to supply water and nutrients. During the growing period, the temperature ranged from 25 to 37∘ C and photosynthetically active radiation (PAR) ranged from 50 to 860 𝜇mol m−2 s−1 . Germination for each accession was recorded seven days after sowing. Plant heights, number of leaves on the main tiller, and days to flowering were visually recorded, and inflorescence architectures were recorded using digital imaging. The average leaf length, leaf width, and vein density of the flag leaf and the penultimate leaves were measured. To study the phenotypic traits, twenty plants from each accession were randomly selected. The maximum width and the vein density at the widest part of the leaf and their lengths were recorded for flag and penultimate leaves. Flowering pattern and duration of flowering in accession A10.1 were studied in detail. 2.1. Setup for Time Lapse Digital Recording. The opening of spikelet and flowering along the panicle were recorded using time lapse recording USB-microscop (...truncated)