Seed Quality

Maturity. The majority of Texas production has shifted to West Texas over the past decade, where climate poses particular problems. The growing season is shorter and time to maturity is longer. Late-season nighttime temperatures of <50° C reduce daytime CO2exchange rates to <50% of optimal, and fruit maturation ceases even though daytime temperatures may be considerably higher. Rapid drying of an immature crop under hot days can result in poor flavor characteristics. Maturity is difficult to estimate in peanut because time to flowering is not a useful indicator of maturity, and because direct observation of pod maturity is not possible without harvesting the plant. Therefore, multiple diggings and evaluations are needed around harvest time. Because early maturity means fewer days for photosynthesis, a correlation between early maturity and reduced yield can be expected.  Therefore, it will be necessary to employ strong selection for both traits.Seed oil content. Seed oxidative stability is associated with oil content. The two predominant oils in the peanut seeds are the monounsaturated 18:1 oleic acid and 18:2 linoleic acid. Oleic acid is significantly more stable to oxidation than is linoleic acid. Typical O/L ratios are 1.7 to 1.8; however, in West Texas, this figure is about 1.2 to 1.3, resulting in a tendency towards rancidity before the end of shelf life for peanuts grown elsewhere. This also contributes to the perception of inferior seed quality.  High-O/L peanut lines can significantly improve shelf life, and contain high levels of the monounsaturated oil oleic acid, associated with reduced coronary artery diesase and present in olive and canola oils.  Two high O/L peanut varieties are being released by  Dr. Charles Simpson(TAES – Stephenville).  These are the runner variety ‘TamRunOL-01’ and the Spanish variety ‘OLin.’For best results, early maturity and high O/L traits need to be combined into a variety.  Development of enhanced O/L peanuts is complicated by the genetics of the O/L trait. Although determined to be controlled by two recessive genes in a runner background, one or two major genes govern the trait in Spanish types, and there is evidence that the genetic nature of this trait is more complex and may be quantitative in nature (López et al., 2000). Mutations in delta-12 desaturase genes have been identified, but genetic association between sequence polymorphisms and oil content has not been tested empirically.
Goals
The primary goal of the breeding program is to develop earlier-maturing peanuts with high yield, enhanced O/L, and disease resistance (see below). Priority is being  given to Spanish and runner types because of their share of the Texas production and time to maturity. We will also attempt to understand better the genetic basis of the high O/L trait to assist in breeding efforts.
Research Program and Results
Maturity.

  • Determination of maturity criteria for West Texas. Standard varieties and advanced breeding material is being grown, harvested in three 2-week intervals, and scored for maturity according to hull color, seed size, yield, and sensory evaluation. The standard method of maturity determination is scraping the pod exodermis and examination of the underlying color.
  • Breeding of early-maturing varieties. We currently have crosses among several Spanish and runner lines, including several high O/L runner lines. We are also crossing early-maturing accessions originating in South America, Africa, and India. F2 and F2:4 selections were made for earliness (Tables 1 and 2), and the best material is being evaluated this summer.
  • Long-term recurrent selection program. This project aims to combine genes for earliness from multiple sources. This offers the possibility of producing varieties that are earlier than is possible by other strategies, but will require several years of development of potential parents.
  • Examine the genetic basis for earliness among accessions. It is expected that there are several different genes for earliness, but also that some different parents may possess the same genes for earliness. We will study the genetics of the early maturity trait and relate it to genetic similarity among with the goal of identifying potential parents that have different genes for earlinesss that can be combined together.
Growth and Digging of Single plants for Maturity Evaluation
Table 1. Summary of F2 Single Plant Maturity Data. 
Maturity was determined by scraping 50 pods per F2 plant and taking note of the hull color. Plants with black hull color were considered to be mature. A range for each population is given. Statistical significance cannot be determined at this stage because data are single F2 plants.

Cross % Black Pods 
(min – avg – max)
Runner High O/L x African Bunch PI 0 – 62 – 100
Runner High O/L x African Bunch PI 0 – 30 – 76
Runner High O/L x African Bunch PI 0 – 56 – 95
Runner High O/L x African Bunch PI 0 – 50 – 100
Runner High O/L x African Bunch PI 0 – 42 – 97
Runner x Runner PI 0 – 17 – 86
Controls
Tamspan90 (Spanish) 38 – 51 – 62
OLin (Spanish) 12 – 25 – 36
TamRunOL01 (Runner) 18 – 21 – 26
Tamrun96 (Runner)
2 – 10 – 16

 

 

 

 

 

 

 

 

growing plantsplowing plants

Table 2. Maturity Classification of F2:4 Plants. 
These are more-advanced materials of older crosses. Each F2:4 was grown out as a single unreplicated 15 foot-long row. Maturity was determined by scraping 50 pods per F2 plant and taking note of the hull color. Plants with black hull color were considered to be mature. A range is given for each population.

Cross or Variety
% Black Pods
(min – avg – max)
Yield in lb/acre
(min – avg – max)
Runner x Runner PI 0 – 27 – 94  593 – 3176 – 6173
Spanish PI X Runner 70 – 80 – 96 1019 – 2771 – 4226
Spanish PI x Spanish 52 – 85 – 95 1280 – 2357 – 2937
Spanish PI x Spanish 73 – 84 – 94 503 – 2392 – 3346
Florunner (Runner) 20 – 26 – 33  263 – 3320 – 6185
Tamspan 90 (Spanish) 76 – 87 – 98  2076 – 4230 – 6384
Virugard (Bunch/Spanish)
48 – 79 – 98
2716 – 3349 – 3212

 

 

 

High-oleic content.

  • Combination with high-oleic lines. Crosses have been made between early-maturing accessions and high-oleic breeding lines, specifically ‘TamRunOL01’ (large-seeded runner) and ‘OLin’ (Spanish). F1‘s are being increased for evaluation next summer.  Material with high O/L ratios and early maturity have been selected and progeny are being evaluated in the field this summer.
  • Determine the genetic nature of the mid-oleic trait. We will use delta-12 desaturase gene sequences from high, middle, and low O/L lines to test association of desaturases and the O/L trait.

References

López, Y., H. L. Nadaf, O. D. Smith, J. P. Connell, A. S. Reddy, and A. K. Fritz. 2000.  Isolation and characterization of the delta-12 fatty acid desaturase in peanut (Arachis hypogaea L.) and search for polymorphism for the high oleate trait in Spanish market-type lines.  Theor. Appl. Genet. 101:1131-1138.

Comments are closed.