Terrell (1968) reports that annual ryegrass is a cross-pollinating specie and is normally thought to be self-incompatible as is perennial ryegrass (L. perenne and L. regidum). These three closely related Lolium species will readily cross with each other as well as fescue (Festuca sp.). All ryegrass taxa are normally diploid with 2n chromosome numbers equaling 14. A number of tetrapoloid varieties have been released in attempting to improve yield and quality of the specie. A large research effort to hybridize ryegrass and fescue (2n = 42) was undertaken at the University of Kentucky several years ago (Webster, 1974). Large numbers of crosses were made which resulted in amphiploids. An amphiploid is a polyploid whose chromosome compliment is made up of the entire somatic compliment of both species. Amphiploids were then backcrossed either to tall fescue or to ryegrass and progeny of these crosses were then tested. Chromosome numbers in the first few generations where often aneuploid (not an even number of either specie), but generally chromosome numbers became stable and new lines were selected out of this breeding program for testing. Results evidently were that these progeny were not significantly improved over original ryegrass parents because no important festoleums are being marketed in the South.

There is a large genetic variability within annual ryegrass populations and in fact because of ryegrass being cross pollinating, there is much variation even within a variety of ryegrass. Because of this variability, ryegrass has the ability to adapt to a wide range of environmental conditions and may be found growing wild around the world. In many regions, it is considered a weed particularly in association with most cool season crops such as wheat. Ryegrass has the ability to escape heat, drought, and floods by going dormant in some cases. It normally persists in areas with hot dry summers as dormant seed.

Annual ryegrass has several common names throughout the world, but for the most part has been called "Italian" ryegrass or "common annua" ryegrass. In Texas, the name "Gulf" or even "Gulf rye" is often used and misused by producers to denote Italian annual ryegrass. These names originated from the variety 'Gulf', the first improved variety, which was released by the Texas Agricultural Experiment Station in 1958 (Weihing, 1963) and has remained popular for the past 37 years. Gulf ryegrass is a direct increase of "La Estanzuela 284", an improved variety from Uruguay. The seed were introduced in 1950 by the Crops Research Division, ARS, USDA, as P.I. 193145 (Holt, 1976). Gulf was first tested in 1952 by the Texas Agricultural Experiment Station and because of its consistent superiority for yield and crown rust (Puccinia coronata) resistance, it was later released. In some parts of the world, ryegrass may be called "Westerwold" ryegrass. This is from a variety or varieties which originated in the Westerwolde area, Province of Groningen, Netherlands. Haan (1955) reported that the Westerwold types were actually Italian ryegrass which had been selected for earliness. There is no indication that the Westerwold ryegrass differs botanically from Italian (annual) ryegrass. The first reported annual ryegrass which was cultivated was grown in northern Italy (Piper, 1935). It was reported in France in 1818 and in Switzerland in 1820. Piper indicates it was imported to England in 1831; however, it may have been present as a weed prior to that date. The actual date annual ryegrass was imported into the USA is not known. Ryegrass was brought to America in early colonial days (Schoth and Weihing, 1962) and has become an important grass.

Annual, common (variety not stated) ryegrass was successfully grown in the Gulf Coast region of the US in the 1940's and 1950's. However, crown rust was often a serious disease problem and reduced forage yields and quality. Plant breeding efforts in Texas, Mississippi, and Florida resulted in the release of crown rust resistant varieties. Texas released Gulf, and Mississippi released 'Magnolia' ryegrass. Both varieties have remained moderately resistant to crown rust and are still available today.

Another major problem with annual ryegrass has been its susceptibility to winterkilling or freeze damage from extreme cold periods during the winter in the southern US. This was to be expected since annual ryegrass had been developed or originated as a spring grass in temperate climates but was being utilized as a winter grass in warmer climates. Plant breeders have selected annual ryegrass as a non-dormant type in the winter. Therefore, tillers must be able to tolerate freezing temperatures while producing rapid vegetative growth when average daily temperatures rise above 50ºF. Cultivars differ in winter hardiness and for length of time for cold hardening to occur (Eagles, 1984). When annual ryegrass has two weeks of temperature near freezing most varieties will be very winter hardy.

In the mid 1970's, Mr. B. L. Arnold, a researcher at the North Mississippi Branch Station at Holly Springs, Mississippi, noticed a stand of volunteer, annual ryegrass, which was thought to be the result of 29 years of natural selection. This selection appeared to be more productive than commercial varieties of ryegrass planted in the autumn. 'Marshall' ryegrass was developed from this population and released in 1981 (Arnold et al., 1981). Marshall was significantly improved for winter hardiness and has extended the range of ryegrass to 200 to 300 miles northward in the US and reduced the threat of winter freeze damage.

To improve winter hardiness in the East Texas ryegrass breeding program, breeding populations were planted on the High Plains near Amarillo, Texas where winter temperatures can be near 0ºF. Germplasm which survived that environment eventually was released in 1991 as 'TAM 90' (Nelson, et al., 1992) and is a winter hardy variety that has cold tolerance similar to Marshall. Since the release of these two varieties as well as others, annual ryegrass acreage has significantly expanded in northeast Texas, Oklahoma, Arkansas, and Tennessee. Varieties of annual ryegrass released in the United States, their origin, and other pertinent information are listed in Table 1 (Balasko, et al., 1995).

New ryegrass breeding objectives:

We have selected for Al tolerance in the seedling stage utilizing the hematoxylin staining procedure (Polle, et al., 1978). In a study comparing the Al tolerant line TX-91-A7 with TAM 90, TX-91-A7 produced a competitive forage yield under acid soil conditions but was not competitive for yield in a limed soil with high nitrogen fertilization (Fig. 1 and 2). Therefore, we either lost some high yielding component in the selection process or we need to go back and select again for high yielding vigor in the Al tolerant population.

Improved reseeding has been incorporated into several of our advanced breeding populations. The screening procedure (Prine, 1982) is relatively easy to conduct and is easily incorporated into ryegrass populations. Seed which germinate at temperatures between 80 and 100ºF are discarded. The seed which do not germinate have a high temperature dormancy gene which delays germination until cooler soil temperatures occur. This prevents ryegrass seed from germinating and dying during the summer months. Our research data indicate that the dormancy character tends to delay early fall growth because much of the seed will not germinate in September or early October. Naturally reseeding ryegrass tends to germinate more slowly (as a population) than present varieties and therefore early forage production is reduced. Even though this character may have an advantage and make naturally reseeding types attractive in grazing systems, it will be difficult to release new varieties because fall yields and total forage production may be reduced.

Some level of fungal endophyte (Acremonium lolii) in annual ryegrass is common in most varieties. For example, our research (Nelson and Ward, 1990 and 1991) indicated that TAM 90, Marshall, Jackson, and Surrey had between 20 and 50% seed infection (Table 2).