INTRODUCTION

Work to improve peach and nectarine cultivars started in New Zealand towards the end of the last century (Glucina and Logan, 1983). Several selections that have become internationally recognized, and used in various breeding programmes, were discovered by raising and evaluating chance seedlings. These included 'Golden Queen' and 'Paragon' peaches and the 'Goldmine' nectarine. These cultivars have proved to be very durable and were important commercial cultivars till the late 1960s. 'Golden Queen' is still the preferred canning peach and 'Goldmine' and 'Paragon' can still be found at some gate sale outlets.

Since the early efforts to improve peaches and nectarines in New Zealand, there have been few attempts to develop new cultivars until the mid-1970s. This is a different situation to that of plum and apricot improvement where many locally selected cultivars have been raised.

In 1976, the then DSIR (now HortResearch) started a programme to improve the 'Golden Queen' peach for the canning industry in Hawkes Bay. Approximately, 5000 seedlings were raised from open-pollinated 'Golden Queen' fruit. Promising lines were tested in a cooperative programme with Watties. Currently, two lines from this programme are now undergoing advanced testing for productivity and canning fruit quality.

Controlled hybridization to produce new cultivars commenced in 1984 and was aimed at producing low acid, white fleshed peaches for Asian markets. Since 1990 the programme has been widened to include other objectives. The aim of this article is to describe the current effort involved with peach and nectarine breeding and the rationale for the programme.

IMPORTED CULTIVARS

From 1976 to 1989, over 70 nectarines and 160 peaches were imported and trialled in various summerfruit growing regions throughout New Zealand and on DSIR research orchards. Some of this work has been reported on (Glucina et al. 1992; Mills et al. 1991). Most of the imported lines were evaluated as cultivars for use by industry while a few selections were imported as germplasm for research use. Today perhaps 10 - 12 of these imported cultivars have become industry standards with several others grown to a lesser extent. The rest failed to make any impact on the industry.

There are several reasons why cultivars fail. These generally involve poor tree adaptability, and fruit productivity and quality in our maritime climate. Often the new cultivars are not superior or sufficiently different to those already commercially grown. The result is that the New Zealand industry relies on a limited range of cultivars with a narrow genetic base, as most were imported from California and tend to have common parents. This becomes important in the context of 'genetic vulnerability' which is shown in the susceptibility of most Californian lines to bacterial diseases in our cooler maritime climate. While these peaches and nectarines tend to be attractive and have good consumer appeal, most tend to have major defects such as limited storage and shelf life. Also lacking are cultivars that mature over an extended period to give a continuity of supply for export markets.

One answer is to the cultivar problem is to continue importing, another is to breed for New Zealand conditions.

PEACH CHARACTERISTICS

The following list includes tree and fruit characteristics that peach breeders have attempted to improve through hybridization and selection. A similar list could be drawn up for nectarines which are essentially smooth skinned peaches.

Although peaches and nectarine cultivars are not as sensitive to climate as apricots, they still require certain conditions to achieve their potential. In particular, chilling hour requirements which determine flowering dates. Flowering dates should be late to minimize frost risk. Generally, in New Zealand, chilling should be at least 600 to 800 chilling hours. Lower chill peaches and nectarines are at great risk from frost damage although there are instances where this type of fruit is successfully grown. The nectarine 'Mayglo' requires only 200 chilling hours. It starts leafing out in June and flowers through July. It can be successfully grown in Hawkes Bay but excellent frost protection is required.

There is a need for greater tree hardiness and disease tolerance. Californian bred peaches and nectarines are particularly susceptible to varying degrees, to the tree and leaf diseases found in New Zealand including bacterial disease (blast and spot), silverleaf and leafcurl. The cultivar 'Rich Lady' for example suffers severely from late infections of bacterial blast. Peach and nectarines can be attacked by several diseases including viruses (peach rosette complex), bacterial diseases and fungal diseases such as leaf curl, brown rot and silver leaf. The cumulative effects of these diseases on tree health are only partially understood but certainly have a debilitating effect on tree productivity as yields in New Zealand are not as high as those reported in other countries.

Better tolerance to rain cracking is also required in nectarines as many cultivars suffered from this defect in moist, humid seasons such as 1992-93.

CURRENT OBJECTIVES

Hybridization is carried out on the Havelock North and Clyde research orchards. Generally, excellent quality seed has been derived from the Clyde site which is also frost protected. As the extended programme is relatively new, seedling numbers are low and initial selection is carried out at Havelock North. As the programme expands, seedlings will also be evaluated at Clyde. The objectives within the breeding programme are:

1. Peaches for the Asian market.
   There is a need to develop suitable white-fleshed peaches with low acidity and high sugar content that are firm, do not bruise easily and store well. These could then be transported to Asian markets where this type of peach is well known. The peach and nectarine collections at the Havelock North Research Centre contain about thirty lines that have been imported from Japan, China and Korea over the last 10 years. Some of these have been evaluated (Glucina et al. 1989). Typically, these peaches tend to be soft and bruise readily. Crosses have been made between this type of peach and lines from the USA that are firmer and have better storage quality. The original crosses for this programme were made by Paul Glucina of DSIR in 1984. One line RGH1/7 ('Redgold' x 'Hakuto') was selected from this material and is currently on trial.
   A non-melting, white-fleshed peach from Korea, 'Yumyeong', has also been used in the breeding programme. 'Yumyeong' fruit store well and appear to have tolerance to brown rot. Progeny from the cross have been evaluated but are generally inferior to current peaches.
   Firmness in peaches has been shown to have low heritability. This means that it will take several generations to increase firmness levels and retain other desired characters. Thus, although this objective appeared straightforward at the start of the programme, developing high quality peaches for this market will take several generations. However, through use of suitable parents it may be possible to obtain good quality lines with intermediate characteristics.
2. Standard yellow-fleshed nectarines.
   Our aim is to breed export quality, mid-season nectarines with improved tree health. Although many lines have been imported they have generally been similar to commercial cultivars such as 'Redgold' and 'Fantasia'. Evaluation has revealed superior cultivars such as 'Zeeglo' in the 'Fantasia' season. However, the success rate of importing new cultivars which are suitable for production in New Zealand is not high for reasons that are discussed above.
   It is possible to breed suitable cultivars that will give a continuity of supply during the export season by crossing high quality Californian lines with more disease-resistant germplasm from the southeastern United States. The material from Georgia and North Carolina shows good tree health in New Zealand, particularly resistance to bacterial diseases. Fruit productivity is high with these lines but fruit colour is not highly developed. Eastern United States cultivars have a yellow background colour and lack the dark red overcolour of most newer Californian cultivars.
3. White-fleshed peaches and nectarines.
   There is increasing interest in white-fleshed peaches and nectarines for export and local market. Several white-fleshed Californian peaches have been trialled in New Zealand. A few such as 'White Lady' and 'Tasty Zee' have gained acceptance. Californian breeders have attempted to improve sugar levels but have tended to produce softer fruit as a result. Again, there is a lack of continuity of peaches of this type through the season. The demand for white-fleshed nectarines is increasing but very few cultivars are available at present. Again, tree health may be improved by using southeastern United States germplasm.
4. Early maturity.
   There are limited numbers of high quality, early maturing peaches and nectarines in New Zealand. Most early maturing fruit are small. Breeding early maturing peaches and nectarines presents some difficulties, as embryos within the stone are immature when the fruit is harvested and embryo rescue techniques are necessary to produce viable seedlings. A small amount of research is being carried out in New Zealand to develop early maturing cultivars.
5. Germplasm.
   Most peaches and nectarine cultivars grown commercially in New Zealand are derived from a very narrow genetic base. An important goal is to increase the germplasm available to the breeding programme by continuing to import material from "non-traditional" areas such as Asia and the southeastern United States. Germplasm is also available from Europe but the presence of the plum pox (sharka) virus makes introductions from this source risky.
   Interspecific hybridization to develop novel peach and nectarine germplasm is a possibility and some material such as 'Citation' rootstock (plum x peach hybrid) has been developed overseas. Embryo rescue techniques could be of advantage, although overseas the most interesting lines have been developed with apricots and plums rather than with peaches.

CONCLUSIONS

Although the peach and nectarine breeding programme is relatively new compared to other fruit improvement programmes which have been developed in New Zealand, the prospects of developing novel, high quality cultivars of peaches and nectarines for the summerfruit industry within the next 5 to 10 years are excellent.

REFERENCES:

Glucina, P.G.; Logan, L.A. 1983: Stone Fruit. Pp 103-110 in Plant Breeding in New Zealand. Wratt, G.S.; Smith, H.C. (ed). Butterworths of New Zealand, Ltd.

Glucina, P.G.; McMath, K.L; Harman, J.E.; Brennan, C.J. 1989: Snow Peaches - the next generation. The Orchardist of New Zealand 62(10):20-26.

Glucina, P.G; Mills, R; King A. 1992: New white fleshed peaches: evaluation of 24 selections. The Orchardist of New Zealand 65(4):44-45.

Mills, R.; Brookfield, P; Glucina P.G; Ross, G. 1991: Peaches and nectarines for the future. The Orchardist of New Zealand 64(6):9-10.