Morphological Variations in Caryopses and Seedlings of Two Grass Species of the Genus Dactyloctenium Willd

Dactyloctenium aegyptium (L.) Willd. and D. aristatum Link. are common grass weeds of cultivated fields in many crops. The two grass weed species growing under similar habitat showed characteristic morphological differences of caryopses and seedlings. The identification of weeds at seedling stage may be useful in weed and environment management. Under the light microscopy, features like colour, base, surface, scutellum and hilum of caryopses showed differences between the studied species. D. aegyptium had dark brown caryopses colour, while D. aristatum had grey colour. The base of D. aegyptium was truncate, while D. aristatum had obtuse base. Both species had rugose surface, but in D. aegyptium surface undulations were closely spaced, whereas in D. Aristatum they were widely spaced. Similarly seedlings were found distinct with respect to coleoptile shape and size, first leaf sheath surface and first leaf blade shape and surface. D. aegyptium had oblong coleoptile, whereas it was obovate in D. aristatum. The leaf sheath and leaf blade were recorded glabrous and hairy in D. aegyptium and in D. aristatum respectively. Both species showed remarkable differentiations in their characters, thus indicating that the morphological attributes of caryopses and seedling can be exploited taxonomically and for crop and weed management.


Introduction
Seed and seedling traits are known to vary strongly across the tropical forest biome in order to cope up with the variations in the distribution and amount of rainfall, light, temperature and soil nutrient regimes. Seedlings of monocots are much more diverse than those of angiosperms, often with much derived characters. Sometimes, this makes morphological interpretation difficult (Tillich, 2007).
Seeds are also important for species identification based on diagnostic features. The seed coat is the outer covering of every mature seed. It is therefore the main modulator of interactions between the internal structure of the seed and the external environment (De Souza and Júlio, 2001).
Caryopsis morphology, as a reliable approach for assessing phylogenetic relationship, had been recognized in Poaceae (Bogdan, 1966;Barthlott, 1981;Wang et al., 1986;Liu et al., 2005). A study revealed that 7 subfamilies corresponded to 7 caryopsis subtypes for Chinese grasses (Wang et al., 1986). In another example, the caryopsis ventral face and embryo shape were valuable characters for recognizing three suprageneric groups in the gramineous subfamily Chloridoideae (Liu et al., 2005). In addition caryopsis shape, dimensions, colour, outline in cross section and surface features were valuable attributes for differentiating 44 species of Indian Eragrostis (Vivek et al., 2015). This is also supported by Hilu and Wright (1982), Terrel and Peterson (1993), Osman et al. (2012) and Gandhi et al. (2016).
Identification of weeds at seedling stage may be useful in weed management with respect to application of weedicides and environment management. In any integrated pest management program, the first logical step is to recognize the pest. Control measures depend upon accurate identification. Grasses occurring as weeds are difficult to identify in their vegetative stages, particularly in the one-to two-leaf Singh and Singh, 1994). At this stage it is important for crop management decisions. Many grasses do not flower until late in the growing season, after they have already had an impact on crop yields. Accurate identification is also important in the early growth stages because smaller grasses are easier to control with conventional management tactics than larger grasses. Smaller grass seedlings are more susceptible to lower dosages of herbicides, and thus greater control can be achieved while minimizing control costs (Bradley and Fishel, 2010).
According to Paria (2014) weed control prefers to focus on the youngest stages of the weeds. Gandhi et al. (2016)

Results
The salient comparative morphological features observed in Dactyloctenium aegyptium and D. aristatum are represented in Fig. 1, Fig. 2 and Table 1. A detailed description of caryopses and seedlings of reported taxa is given below along with description of mature plant.
In the present study, two grass species (Dactyloctenium aegyptium and D. aristatum) of the same genus Dactyloctenium Willd., growing in the same habitat, have been evaluated for morphological features of caryopses and seedlings and their taxonomic significance.
The two grass weed species (Dactyloctenium aegyptium and D. aristatum) are found commonly in the cultivated fields of the area. They were also found on road sides and on rocks. Collected specimens were dissected and identified with the help of different floras (Moulik, 1997;Singh, 2007). Identified species were further confirmed from Herbarium, Botanical Survey of India (Central Regional Centre, BSA), Allahabad, Uttar Pradesh, India. Voucher specimens have been deposited in the Herbarium, Department of Botany, Udai Pratap College (Autonomous), Varanasi, India.

Caryopses morphology
Caryopses were collected from mature spikelets. Mature caryopses were manually separated from the spikelets and used for the microscopic studies. Samples of 15-20 dried caryopses for each species were examined under Stereo Microscope (Olympus-Magnus MSZ-TR), photographed and described following Gandhi et al. (2016).

Seedling morphology
For the morphological observations on seedlings, caryopses have been grown in petri dishes (20 × 5 cm) on moist filter paper at 22-24 o C in permanent light and in sandy soil in the green house and described as per Singh et al. (2016). Morphological features of mature specimens along with differentiation at mature and at seedling stage (Table 1) and illustrations ( Fig. 1 and Fig. 2) have also been provided.   The caryopses is ovoid-quadrangular in outline, 0.07 × 0.05 cm, mean L/W 1.4, base truncate, apex rounded, and laterally compressed, reddish-brown, surface rugose with widely spaced undulations. The scutellum is ovate, 0.10 × 0.05 cm, mean L/W 2, base and apex rounded, flat and glabrous. The hilum is oval.
The seedling germination was mesogeal. The primary root was fibrous, branched, dull white, hairy; hair base broad, apex acute, transparent; 1.5 cm long at coleoptile stage, 2.0 cm, 2.5 cm and 3.0 cm long at 1 st , 2 nd and at 3 rd leaf stages respectively. The collet was distinct, dull white, swollen, hairy; hairs base broad, apex acute, transparent, 0.2 cm long. The epiblast was swollen, distinct with mesocotyl. The mesocotyl was light green, glabrous, terete, 0.5 cm long. The coleoptile was oblong, 0.90 x 0.15 cm, mean L/W 6.0, base truncate, apex acute, green, membranous, glabrous, binerved; nerves green, distinct, parallel. The adventitious roots were present at coleoptile stage. The first leaf sheath was green, membranous, glabrous and compressed, margins entire, hyaline, glabrous, 0.5 cm long. The ligule was membranous; base truncate, apex rounded, glabrous, 0.6 cm long. The first leaf blade was obovate, 1.8 x 0.4 cm, mean L/W 4.5, base cuneate, apex obtuse, the margins were denticulate, green, membranous and glabrous, veins 5. The second leaf sheath was green, membranous, enrolled, much compressed, glabrous, with entire margins, 0.6 cm long. The ligule was same as the first leaf. The second leaf blade was lanceolate, 2.5 × 0.5 cm, the mean L/W was 5.0, base truncate, apex acuminate, the margins and surface was same as first leaf, and 5 veins were present.
The common names of Dactyloctenium aegyptium are: beach wiregrass, crowfoot grass, coast button grass, comb fringe grass, duck grass, Durban crowfoot, Egyptian finger grass, Egyptian grass and it blooms during May-October.
Dactyloctenium aegyptium is distributed in North Kenya to Sudan, and eastwards through Arabia to India, Pakistan.
The caryopses is ovoid-quadrangular in outline, 0.1 x 0.08 cm, the mean L/W is 1.2, base obtuse, apex rounded, laterally compressed, gray in colour, surface rugose with narrowly spaced undulations. The scutellum is ovate, 0.05 x 0.03 cm, mean L/W 1.6, base and apex rounded, flat and glabrous. The hilum is oval.
The seedling germination was mesogeal. The primary roots were fibrous, branched, dull white, terete, 1.5 cm long at coleoptile stage, 2.0 cm, 2.5 cm and 3.0 cm long at 1 st , 2 nd and at 3 rd leaf stages respectively. The collet was dull white, slightly swollen, hairy; hair base broad, apex acute, transparent, 0.2 cm long. The epiblast was slightly swollen, surface undulate, dull white, glabrous. The mesocotyl was light green, glabrous, terete, 0.6 cm long. The coleoptile was obovate, 1.0 x 0.2 cm, the mean L/W was 5.0, base truncate, apex acute, green, membranous, glabrous, binerved; nerves green, distinct, and parallel. The adventitious roots was present at coleoptile stage. The first leaf sheath was green, membranous, hairy; hair base broad, apex acute, transparent, 0.2 cm long; margins entire, 0.5 cm long. The ligule was present at 2 nd leaf stage. The first leaf blade was elliptical, 0.6 x 0.3 cm, the mean L/W was 2, base cuneate, apex acute, margins denticulate, green, pubescent; hairs as on leaf sheath; veins 7. The second leaf sheath was same as the first leaf. The ligule was membranous, base truncate, apex obtuse, margins entire, 0.2 cm long. The second leaf blade was oblong, 1.0 x 0.4 cm, the mean L/W was 2.5, base cuneate, apex acute, the margins and the surface was same as the first leaf blade with 7 veins.
Dactylocteniumaristatum is distribuited inNorth Kenya to Sudan and east wards through Arabia to India and Pakistan and it blooms during September-November.

Caryopses features
Light microscopic features of D. aegyptium and D. aristatum revealed few similar features. Both are ovoid quadrangular in shape. They had ovate scutellum, belong to the small type of embryo (embryo % was less than 46%). Both species showed ovate scutellum but differ with respect to length. A marked difference was noted in the colour, base, surface and hilum of the two species as D. aegyptium had dark brown colour, while D. aristatum had grey colour. The base of D. aegyptium was truncate, while D. aristatum had obtuse base. Both the taxa had rugose surface but in D. aegyptium surface undulations were closely spaced whereas in D. aristatum it was widely spaced. The hilum was found distinct in shape i.e. oval and circular in D. aegyptium and D. aristatum respectively (Fig 2, Table 1). Liu et al. (2005) also studied and revealed that caryopsis morphology in Chlorideae is significant. The current observations were found similar to Zhang et al. (2014). The authors reported that caryopsis shapes, embryo proportions, and sculpturing patterns were valuable diagnostic characters at the interspecific level in Themeda. In a recently study, Vivek et al. (2015) observed the caryopsis morphology of Ergrostis in India representing 44 species and reported their morphological significance. Similar observations have been made by many workers. Hilu and Wright (1982) discussed phylogenetic relationship of tribe Chlorideae, mainly on the basis of morphological and molecular data. Terrel and Peterson (1993) studied the caryopsis morphology of tribe Triticeae to evaluate the morphological structure of the caryopses within Triticeae and divided the tribe into two major subtribes. Osman et al. (2012) studied the fruit morphology of 33 annual grass species from Egypt belonging to 24 genera and 11 tribes. Gandhi et al. (2016) published a book on the identification and characterization of caryopsis and seedlings.

Seedlings features
The seedling morphology of reported grass weed taxa showed some interesting diagnostic attributes viz. coleoptile, First leaf sheath and First leaf blade (Fig 1A, 1B; Table 1). On the basis of these attributes the reported taxa D. aegyptium and D. aristatum can be easily differentiated and identified at seedling stage. However, they were also clearly distinct at maturity with respect to leaf sheath, prophyllum, ligule, number of spikes, number of florets in spikelets, lower glume and upper glume (Fig 1A, 1B, Fig  2A1, 2B1, Table 1). The coleoptile shape, and the shape and surface of first leaf sheath and first leaf blade of the reported taxa showed clear cut distinction and these attributes are found significant. As it is evident from Fig. 1A9, 1B9 and Table 1, D. aegyptium had oblong coleoptile whereas it was obovate in D. aristatum. Similarly leaf sheath and leaf blade were recorded glabrous and hairy in D. aegyptium and in D. aristatum respectively. The shape of the first leaf blade was obovate and elliptical in D. aegyptium and D. aristatum respectively (Fig. 1A7, 1B7, Table 1). The previous observations on this line by Kuwabara (1960Kuwabara ( , 1961, Jian-Guo et al. (1993), Singh and Singh (1994); Durgan (1999); Wintel et al. (2009);Harries (2010); ; ; Gandhi et al. (2016) and Singh et al. (2016) are found supportive in the sense of present observation.

Conclusions
The caryopsis and the seedling morphological characters were valuable diagnostic characters at the interspecific level and morphological attributes of grass. The caryopsis and seedlings of D. aegyptium and D. aristatum can be exploited from taxonomic point of view and for crop weed management.